Questions · Page 4 of 13

MCQ

MCQ 1511 Mark
Let $P=\{z \in \mathbb{C}:|z+2-3 i| \leq 1\}$ and $Q=\{z \in \mathbb{C}: z(1+i)+\bar{z}(1-i) \leq-8\}$. Let in $\mathrm{P} \cap \mathrm{Q},|\mathrm{z}-3+2 \mathrm{i}|$ be maximum and minimum at $z_1$ and $z_2$ respectively. If $\left|z_1\right|^2+2|z|^2=\alpha+\beta \sqrt{2}$, where $\alpha, \beta$ are integers, then $\alpha+\beta$ equals______.
  • A
    $30$
  • B
    $35$
  • $36$
  • D
    $40$
Answer
Correct option: C.
$36$
c
Clearly for the shaded region $z_1$ is the intersection of the circle and the line passing through $\mathrm{P}\left(\mathrm{L}_1\right)$ and $\mathrm{z}_2$ is intersection of line $\mathrm{L}_1 \& \mathrm{~L}_2$

Circle : $(x+2)^2+(y-3)^2=1$

$L_1: x+y-1=0 $

$L_2: x-y+4=0$

On solving circle $\mathrm{L}_1$ we get

$z_1:\left(-2-\frac{1}{\sqrt{2}}, 3+\frac{1}{\sqrt{2}}\right)$

On solving $\mathrm{L}_1$ and $\mathrm{z}_2$ is intersection of line $\mathrm{L}_1 \& \mathrm{~L}_2$ we get $z_2:\left(\frac{-3}{2}, \frac{5}{2}\right)$

$\left|z_1\right|^2+2\left|z_2\right|^2=14+5 \sqrt{2}+17$

$=31+5 \sqrt{2}$

So  $\alpha=31$

$\beta=5$

$\alpha+\beta=36$

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MCQ 1521 Mark
The area (in sq. units) of the region $\mathrm{S}=\{\mathrm{z} \in \mathbb{C} ;|\mathrm{z}-1| \leq 2 ;(\mathrm{z}+\overline{\mathrm{z}})+\mathrm{i}(\mathrm{z}-\overline{\mathrm{z}}) \leq 2, \operatorname{lm}(\mathrm{z}) \geq 0\}$ is
  • A
     $\frac{7 \pi}{3}$
  • $\frac{3 \pi}{2}$
  • C
    $\frac{17 \pi}{8}$
  • D
    $\frac{7 \pi}{4}$
Answer
Correct option: B.
$\frac{3 \pi}{2}$
b
Put $z=x+i y$

$ |z-1| \leq 2 \Rightarrow(x-1)^2+y^2 \leq 4 $

$ (z+\bar{z})+i(z-\bar{z}) \leq 2 \Rightarrow 2 x+i(2 i y) \leq 2 $

$ \Rightarrow x-y \leq 1 $

$ \operatorname{Im}(z) \geq 0 \Rightarrow y \geq 0$

$Image$

Required area

Area of semi-circle - area of sector A

$ \frac{1}{2} \pi(2)^2-\frac{\pi}{2} $

$ =\frac{3 \pi}{2}$

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MCQ 1531 Mark
Let $S_1=\{z \in C:|z| \leq 5\}$,

$S_2=\left\{z \in C: I m\left(\frac{z+1-\sqrt{3} i}{1-\sqrt{3} i}\right) \geq 0\right\}$ and

$\mathrm{S}_3=\{\mathrm{z} \in \mathrm{C}: \operatorname{Re}(\mathrm{z}) \geq 0\}$. Then

  • A
     $\frac{125 \pi}{6}$
  • B
     $\frac{125 \pi}{24}$
  • C
     $\frac{125 \pi}{4}$
  • $\frac{125 \pi}{12}$
Answer
Correct option: D.
$\frac{125 \pi}{12}$
d
$ S_1: x^2+y^2 \leq 25 $

$ S_2: \operatorname{Im} \text { of } \frac{z+(1-\sqrt{3} i)}{(1-\sqrt{3} i)} \geq 0 $

$ \operatorname{Im} \text { of }\left(\frac{x+i y}{1-\sqrt{3} i}+1\right) \geq 0 $

$ \operatorname{Im} \text { of }\left(\frac{(x+i y)(1+\sqrt{3} i)}{4}\right) \geq 0 $

$ \Rightarrow \sqrt{3} x+y \geq 0 $

$ S_3: x \geq 0 $

$ \text { Area }=\frac{5}{12}\left(\pi(5)^2\right)$

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MCQ 1541 Mark
If $z_1, z_2$ are two distinct complex number such that $\left|\frac{z_1-2 z_2}{\frac{1}{2}-z_1 \bar{z}_2}\right|=2$, then
  • either $z_1$ lies on a circle of radius 1 or $z_2$ lies on a circle of radius $\frac{1}{2}$
  • B
    either $z_1$ lies on a circle of radius $\frac{1}{2}$ or $z_2$ lies on a circle of radius $1$ .
  • C
    $z_1$ lies on a circle of radius $\frac{1}{2}$ and $z_2$ lies on a circle of radius $1$ .
  • D
     both $z_1$ and $z_2$ lie on the same circle.
Answer
Correct option: A.
either $z_1$ lies on a circle of radius 1 or $z_2$ lies on a circle of radius $\frac{1}{2}$
a
$ \frac{z_1-2 z_2}{\frac{1}{2}-z_1 \bar{z}_2} \times \frac{\bar{z}_1-2 \bar{z}_2}{\frac{1}{2}-\bar{z}_1 z_2}=4 $

$ \left|z_1\right|^2 2 z_1 \bar{z}_2-2 \bar{z}_1 z_2+4\left|z_2\right|^2 $

$ =4\left(\frac{1}{4}-\frac{\bar{z}_1 z_2}{2}-\frac{z_1 \bar{z}_2}{2}+\left|z_1\right|^2\left|z_2\right|^2\right)$

$\mathrm{z}_1 \overline{\mathrm{z}}_1+2 \mathrm{z}_2 \cdot 2 \overline{\mathrm{z}}_2-\mathrm{z}_1 \overline{\mathrm{z}}_1 2 \mathrm{z}_2 2 \overline{\mathrm{z}}_2-1=0$

$ \left(z, \bar{z}_1-1\right)\left(1-2 z_2 \cdot 2 \bar{z}_2\right)=0 $

$ \left(\left|z_1\right|^2-1\right)\left(\left|2 z_2\right|^2-1\right)=0$

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MCQ 1551 Mark
The sum of the square of the modulus of the elements in the set

$\{z=a+i b: a, b \in Z, z \in C,|z-1| \leq 1,|z-5| \leq|z-5 i|\}$ is ........

  • A
    $10$
  • $9$
  • C
    $5$
  • D
    $12$
Answer
Correct option: B.
$9$
b
$ |z-1| \leq 1 $

$ \Rightarrow|(x-1)+i y| \leq 1 $

$ \Rightarrow \sqrt{(x-1)^2+y^2} \leq 1 $

$ \Rightarrow(x-1)^2+y^2 \leq 1 ............(1)$

Also $|z-5| \leq|z-5 i|$

$ (x-5)^2+y^2 \leq x^2+(y-5)^2 $

$ -10 x \leq-10 y $

$ \Rightarrow x \geq y.........(2)$

Solving ($1$) and ($2$)

$ \Rightarrow(\mathrm{x}-1)^2+\mathrm{x}^2=1 $

$ \Rightarrow 2 \mathrm{x}^2-2 \mathrm{x}=0 $

$ \Rightarrow \mathrm{x}(\mathrm{x}-1)=0 $

$ \Rightarrow \mathrm{x}=0 \text { or } \mathrm{x}=1 $

$ \mathrm{y}=0 \text { or } \mathrm{y}=1$

$Image$

Given $\mathrm{x}, \mathrm{y} \in \mathrm{I}$

Points $(0,0),(1,0),(2,0),(1,1),(1,-1)$ to find

$\left|z_1\right|^2+\left|z_2\right|^2+\left|z_3\right|^2+\left|z_4\right|^2+\left|z_5\right|^2 $

$ =0+1+4+1+1+1+1=9$

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MCQ 1561 Mark
Let $z$ be a complex number such that the real part of $\frac{z-2 i}{z+2 i}$ is zero. Then, the maximum value of $|\mathrm{z}-(6+8 \mathrm{i})|$ is equal to :
  • $12$
  • B
    $\infty$
  • C
    $10$
  • D
    $8$
Answer
Correct option: A.
$12$
a
$ \frac{z-2 i}{z+2 i}+\frac{\bar{z}+2 i}{\bar{z}-2 i}=0 $

$ z \bar{z}-2 i \bar{z}-2 i z+4(-1) $

$ +z \bar{z}+2 z i+2 \bar{z} i+4(-1)=0 $

$ \Rightarrow 2|z|^2=8 \Rightarrow|z|=2 $

$ |z-(6+8 i)|_{\text {maximum }}=10+2=12$

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MCQ 1571 Mark
If $\alpha$ satisfies the equation $x^2+x+1=0$ and $(1+\alpha)^7=\mathrm{A}+\mathrm{B} \alpha+\mathrm{C}^2, \mathrm{~A}, \mathrm{~B}, \mathrm{C} \geq 0$, then $5(3 A-2 B-C)$ is equal to..........................
  • A
    $6$
  • $5$
  • C
    $7$
  • D
    $3$
Answer
Correct option: B.
$5$
b
$x^2+x+1=0 \Rightarrow x=\omega, \omega^2=\alpha$

Let $\alpha=\omega$

Now $(1+\alpha)^7=-\omega^{14}=-\omega^2=1+\omega$

$ A=1, B=1, C=0 $

$ \therefore 5(3 A-2 B-C)=5(3-2-0)=5$

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MCQ 1581 Mark
Let $\alpha, \beta$ be the roots of the equation $x^2-\sqrt{6} x+3=0$ such that $\operatorname{Im}(\alpha)>\operatorname{Im}(\beta)$. Let $a, b$ be integers not divisible by $3$ and $n$ be a natural number such that $\frac{\alpha^{99}}{\beta}+\alpha^{98}=3^n(a+i b), i=\sqrt{-1}$. Then $\mathrm{n}+\mathrm{a}+\mathrm{b}$ is equal to_.....................
  • $49$
  • B
    $42$
  • C
    $45$
  • D
    $59$
Answer
Correct option: A.
$49$
a
$ x^2-\sqrt{6} x+6=0 $

$ x=\frac{\sqrt{6} \pm i \sqrt{6}}{2}=\frac{\sqrt{6}}{2}(1 \pm i) $

$ \alpha=\sqrt{3}\left(e^{i \frac{\pi}{4}}\right), \beta=\sqrt{3}\left(e^{-i \frac{\pi}{4}}\right) $

$ \therefore \frac{\alpha^{99}}{\beta}+\alpha^{98}=\alpha^{98}\left(\frac{\alpha}{\beta}+1\right) $

$ =\frac{\alpha^{98}(\alpha+\beta)}{\beta}=3^{49}\left(e^{i 99 \frac{\pi}{4}}\right) \times \sqrt{2} $

$ =3^{49}(-1+i) $

$ =3^n(a+i b) $

$ \therefore n=49, a=-1, b=1$

$ \therefore n+a+b=49-1+1=49$

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MCQ 1591 Mark
If $\mathrm{z}$ is a complex number, then the number of common roots of the equation $z^{1985}+z^{100}+1=0$ and $z^3+2 z^2+2 z+1=0$, is equal to :
  • A
    $1$
  • $2$
  • C
    $0$
  • D
    $3$
Answer
Correct option: B.
$2$
b
$z^{1985}+z^{100}+1=0 \quad \& z^3+2 z^2+2 z+1=0 $

$(z+1)\left(z^2-z+1\right)+2 z(z+1)=0$

 $(z+1)\left(z^2+z+1\right)=0$

$\begin{aligned} & (\mathrm{z}+1)\left(\mathrm{z}^2+\mathrm{z}+1\right)=0 \\ \Rightarrow \quad & \mathrm{z}=-1, \mathrm{z}=\mathrm{w}, \mathrm{w}^2\end{aligned}$

Now put $\mathrm{z}=\mathrm{w}$

$\begin{array}{ll}\Rightarrow & \mathrm{w}^{1985}+\mathrm{w}^{100}+1 \\ \Rightarrow & \mathrm{w}^2+\mathrm{w}+1=0 \\ & \text { Also, } \mathrm{z}=\mathrm{w}^2 \\ \Rightarrow & \mathrm{w}^{3970}+\mathrm{w}^{200}+1 \\ \Rightarrow & \mathrm{w}+\mathrm{w}^2+1=0\end{array}$

Two common root

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MCQ 1601 Mark
Let the complex number $z=x+$ iy be such that $\frac{2 z-3 i}{2 z+i}$ is purely imaginary. If $x + y ^2=0$, then $y^4+y^2-y$ is equal to :
  • A
    $\frac{3}{2}$
  • B
    $\frac{4}{3}$
  • C
    $\frac{2}{3}$
  • $\frac{3}{4}$
Answer
Correct option: D.
$\frac{3}{4}$
d
$\frac{2 z-3 i}{2 z+i}$ is purely imaginary

$\therefore \frac{2 z-3 i}{2 z+i}+\frac{2 \bar{z}+3 i}{2 \bar{z}-i}=0$

$z=x+i y$

$\Rightarrow 4 x^2+4 y^2-4 y-3=0$

Given that $x+y^2=0$

$y^4+y^2-y=3 / 4$

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MCQ 1611 Mark
Let $\quad S=\left\{z=x+i y: \frac{2 z-3 i}{4 z+2 i}\right.$ is a real number $\}$. Then which of the following is NOT correct?
  • A
    $y + x ^2+ y ^2 \neq-\frac{1}{4}$
  • B
    $x=0$
  • $( x , y )=\left(0,-\frac{1}{2}\right)$
  • D
    $y \in\left(-\infty,-\frac{1}{2}\right) \cup\left(-\frac{1}{2}, \infty\right)$
Answer
Correct option: C.
$( x , y )=\left(0,-\frac{1}{2}\right)$
c
$\frac{2 z-3 i}{q z+2 i} \in R$

$\frac{2(x+i y)-3 i}{4(x+i t)+2 i}=\frac{2 x+(2 y-3) i}{4 x+(4 y+2) i} \times \frac{4 x-(4 y+2) i}{4 x-(4 y+2) i}$

$4 x(2 y-3)-2 x(4 y+2)=0$

$x=0 \quad y \neq-\frac{1}{2}$

$\text { Ans. }=3$

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MCQ 1621 Mark
Let $A =\left\{\theta \in(0,2 \pi): \frac{1+2 i \sin \theta}{1- i \sin \theta}\right.$ is purely imaginary $\}$. Then the sum of the elements in $A$ is
  • A
    $\pi$
  • B
    $2 \pi$
  • $4 \pi$
  • D
    $3 \pi$
Answer
Correct option: C.
$4 \pi$
c
$z=\frac{1+2 i \sin \theta}{1-i \sin \theta} \times \frac{1+i \sin \theta}{1+i \sin \theta}$

$z=\frac{1-2 \sin ^2 \theta+i(3 \sin \theta)}{1+\sin ^2 \theta}$

$\operatorname{Re}(z)=0$

$\frac{1-2 \sin ^2 \theta}{1+\sin ^2 \theta}=0$

$\sin \theta=\frac{ \pm 1}{\sqrt{2}}$

$A=\left\{\frac{\pi}{4}, \frac{3 \pi}{4}, \frac{5 \pi}{4}, \frac{7 \pi}{4}\right\}$

$\text { sum }=4 \pi(\text { Option } 3)$

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MCQ 1631 Mark
For two non-zero complex number $z_1$ and $z_2$, if $\operatorname{Re}\left(z_1 z_2\right)=0$ and $\operatorname{Re}\left(z_1+z_2\right)=0$, then which of the following are possible ?

$(A)$ $\operatorname{Im}\left(z_1\right) > 0$ and $\operatorname{Im}\left(z_2\right) > 0$

$(B)$ $\operatorname{Im}\left(z_1\right) < 0$ and $\operatorname{Im}\left(z_2\right) > 0$

$(C)$ $\operatorname{Im}\left(z_1\right) > 0$ and $\operatorname{Im}\left(z_2\right) < 0$

$(D)$ $\operatorname{Im}\left( z _1\right) < 0$ and $\operatorname{Im}\left( z _2\right) < 0$

Choose the correct answer from the options given below :

  • A
    $B$ and $D$
  • $B$ and $C$
  • C
    $A$ and $B$
  • D
    $A$ and $C$
Answer
Correct option: B.
$B$ and $C$
b
$z _1= x _1+ i y _1$

$z _2= x _2+ iy _2$

$\operatorname{Re}\left(z_1 z_2\right)=x_1 x_2-y_1 y_2=0$

$\operatorname{Re}\left(z_1+z_2\right)=x_1+x_2=0$

$x_1$ and $x_2$ are of opposite sign

$y_1$ and $y_2$ are of opposite sign

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MCQ 1641 Mark
Let $\alpha=8-14 i , A=\left\{ z \in C : \frac{\alpha z -\bar{\alpha} \overline{ z }}{ z ^2-(\overline{ z })^2-112 i }=1\right\}$ and $B =\{ z \in C :| z +3 i |=4\}$ Then $\sum_{z \in A \cap B}(\operatorname{Re} z-\operatorname{Im} z)$ is equal to $...............$.
  • $14$
  • B
    $13$
  • C
    $12$
  • D
    $11$
Answer
Correct option: A.
$14$
a
$\alpha=8-14 i$

$z=x+i y$

$a z=(8 x+14 y)+i(-14 x+8 y)$

$z +\overline{ z }=2 x \quad z -\overline{ z }=2 iy$

Set A: $\frac{2 i(-14 x+8 y)}{i(4 x y-112)}=1$

$(x-4)(y+7)=0$

$x=4 \quad \text { or } \quad y=-7$

Set B: $x^2+(y+3)^2=16$

when $x=4 \quad y=-3$

when $y =-7 \quad x =0$

$\therefore A \cap B=\{4-3 i, 0-7 i\}$

So, $\sum_{z \in A \cap B}(\operatorname{Re} z-\operatorname{Im} z)=4-(-3)+(0-(-7))=14$

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MCQ 1651 Mark
Let $z =1+ i$ and $z _1=\frac{1+ i \overline{ z }}{\overline{ z }(1- z )+\frac{1}{ z }}$. Then $\frac{12}{\pi}$ $\arg \left(z_1\right)$ is equal to $..........$.
  • A
    $18$
  • B
    $27$
  • C
    $36$
  • $9$
Answer
Correct option: D.
$9$
d
$z=1+i$

$z_1=\frac{1+i \bar{z}}{\bar{z}(1-z)+\frac{1}{z}}$

$z_1=\frac{1+i(1-i)}{(1-i)(1-1-i)+\frac{1}{1+i}}$

$=\frac{1+i-i^2}{(1-i)(-i)+\frac{1-i}{2}}$

$=\frac{2+i}{-3 i-1}=\frac{4+2 i}{-3 i-1}$

$=\frac{-(4+2 i)(3 i-1)}{(3 i)^2-(1)^2}$

$\therefore \frac{12}{\pi} \arg \left(z_1\right)=\frac{12}{\pi} \times \frac{3 \pi}{4}=9$

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MCQ 1661 Mark
Let $a \neq b$ be two non-zero real numbers.Then the number of elements in the set $X =\left\{ z \in C : \operatorname{Re}\left(a z^2+ bz \right)= a \text { and }\operatorname{Re}\left(b z^2+ az \right)= b \right\}$ is equal to
  • A
    $1$
  • B
    $3$
  • $0$
  • D
    $2$
Answer
Correct option: C.
$0$
c
$\operatorname{Re}\left(a z^2+b z\right)=a$

$a z^2+b z+a \bar{z}^2+b \bar{z}=2 a$

$a\left(z^2+\bar{z}^2\right)+ b ( z +\overline{ z })=2 a$

$\operatorname{Re}\left( bz z^2+ az \right)= b$

$b z^2+a z+b \bar{z}^2+ az =2 b$

$b \left( z ^2+\overline{ z }^2\right)+ a ( z +\overline{ z })=2 b$

$(1) \times b-(2) \times(a)$

$\Rightarrow\left(b^2-a^2\right)(z+\bar{z})=0$

$\Rightarrow \quad(z+\bar{z})=0 \quad\left(a^2 \neq b^2\right)$

$(1) \times a-(2) \times(b)$

$\Rightarrow \quad\left(a^2-b^2\right)(z+\bar{z})=2\left(a^2-b^2\right) \quad\left(a^2 \neq b^2\right)$

$z^2+\bar{z}^2=2$

$\Rightarrow(z+\bar{z})^2-2 z \bar{z}=2$

$z \bar{z}=-1$

$\Rightarrow 1+1^2=-1$

$\Rightarrow \text { No solution }$

$\text { But when } a=-b$

$\operatorname{Re}\left(a z^2-a z\right)=a$

$\Rightarrow \quad \operatorname{Re}\left(a\left(x^2-y^2+i 2 x y\right)-a(x+i y)\right)=a$

$\Rightarrow a\left(x^2-y^2\right)-a x=a$

$\Rightarrow x^2-y^2-x=1$

$\Rightarrow x^2-x-1=y^2$

For any real values of $y$ there two values of $x$, hence infinite complex numbers are possible.

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MCQ 1671 Mark
If for $z=\alpha+i \beta,|z+2|=z+4(1+i)$, then $\alpha+\beta$ and $\alpha \beta$ are the roots of the equation
  • $x^2+7 x+12=0$
  • B
    $x^2+3 x-4=0$
  • C
    $x^2+2 x-3=0$
  • D
    $x ^2+ x -12=0$
Answer
Correct option: A.
$x^2+7 x+12=0$
a
$|z+2|=|\alpha+i \beta+2|$

$=\alpha+i \beta+4+4 i$

$\sqrt{(\alpha+2)^2+\beta^2}=(\alpha+4)+ i (\beta+4)$

$\beta+4=0$

$(\alpha+2)^2+16=(\alpha+4)^2$

$\beta=-4$

$\alpha^2+4+4 \alpha+16=\alpha^2+16+8 \alpha$

$4=4 \alpha$

$\alpha=1$

$\alpha=1, \beta=-4$

$\alpha+\beta=-3, \alpha \beta=-4$

$\text { Sum of roots }=-7$

$\text { Product of roots }=12$

$x^2+7 x+12=0$

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MCQ 1681 Mark
For $a \in C$, let $A =\{z \in C: \operatorname{Re}( a +\overline{ z }) > \operatorname{Im}(\bar{a}+z)\}$ and $B=\{z \in C: \operatorname{Re}(a+\bar{z}) < \operatorname{Im}(\bar{a}+z)\}$. Then among the two statements :

$(S 1)$ : If $\operatorname{Re}(A), \operatorname{Im}(A) > 0$, then the set $A$ contains all the real numbers

$(S2)$: If $\operatorname{Re}(A), \operatorname{Im}(A) < 0$, then the set $B$ contains all the real numbers,

  • A
    Only $(S1)$ is true
  • both are false
  • C
    Only $(S2)$ is true
  • D
    Both are true
Answer
Correct option: B.
both are false
b
Let $a=x_1+i y_1 z=x+i y$

Now $\operatorname{Re}(a+\bar{z}) > \operatorname{Im}(\bar{a}+z)$

$\therefore x _1+ x >- y _1+ y$

$x _1=2, y _1=10, x =-12, y =0$

Given inequality is not valid for these values.

$S 1$ is false.

Now $\operatorname{Re}(a+\bar{z})<\operatorname{Im}(\bar{a}+z)$

$x _1+ x < - y _1+ y$

$x _1=-2, y _1=-10, x =12, y =0$

Given inequality is not valid for these values.

$S2$ is false.

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MCQ 1691 Mark
Let $S=\left\{Z \in C: \bar{z}=i\left(z^2+\operatorname{Re}(\bar{z})\right)\right\}$. Then $\sum_{z \in S}|z|^2$ is equal to
  • A
    $\frac{7}{2}$
  • $4$
  • C
    $\frac{5}{2}$
  • D
    $3$
Answer
Correct option: B.
$4$
b
Let $Z=x+$ iy, $x \in R, y \in R$

$x-i y=i\left(x^2-y^2+(2 x y) i+x\right)$

$x =- 2 x x$

$- y =- y ^2+ x ^2+ x$

$\Rightarrow x=0, y=-\frac{1}{2}(\text { from }(1))$

If $x \neq 0$, then $y =0,1$

If $y =-\frac{1}{2}$, then $x =\frac{1}{2},-\frac{3}{2}$

$Z =0+ i 0,0+ i , \frac{1}{2}-\frac{ i }{2},-\frac{3}{2}-\frac{ i }{2}$

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MCQ 1701 Mark
If the set $\left\{\operatorname{Re}\left(\frac{z-\bar{z}+z \bar{z}}{2-3 z+5 \bar{z}}\right): z \in C , \operatorname{Re}(z)=3\right\}$ is equal to the interval $(\alpha, \beta]$, then $24(\beta-\alpha)$ is equal to
  • A
    $36$
  • B
    $42$
  • C
    $27$
  • $30$
Answer
Correct option: D.
$30$
d
Let $z_1=\left(\frac{z-\bar{z}+z \bar{z}}{2-3 z+5 \bar{z}}\right)$

Let $z=3+i y$

$\bar{z}=3-i y$

$z_1=\frac{2 i y+\left(9+y^2\right)}{2-3(3+i y)+5(3-i y)}$

$=\frac{9+y^2+i(2 y)}{8-8 i y}$

$=\frac{\left(9+y^2\right)+i(2 y)}{8(1-i y)}$

$\operatorname{Re}\left(z_1\right)=\frac{\left(9+y^2\right)-2 y^2}{8\left(1+y^2\right)}$

$=\frac{9-y^2}{8\left(1+y^2\right)}$

$=\frac{1}{8}\left[\frac{10-\left(1+ y ^2\right)}{\left(1+ y ^2\right)}\right]$

$=\frac{1}{8}\left[\frac{10}{1+ y ^2}-1\right]$

$1+ y ^2 \in[1, \infty]$

$\frac{1}{1+ y ^2} \in(0,1]$

$\frac{10}{1+ y ^2} \in(0,10]$

$\frac{10}{1+ y ^2}-1 \in(-1,9]$

$\operatorname{Re}\left( z _1\right) \in\left(\frac{-1}{8}, \frac{9}{8}\right]$

$\alpha=\frac{-1}{8}, \beta=\frac{9}{8}$

$24(\beta-\alpha)=24\left(\frac{9}{8}+\frac{1}{8}\right)=30$

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MCQ 1711 Mark
The complex number $z=\frac{i-1}{\cos \frac{\pi}{3}+i \sin \frac{\pi}{3}}$ is equal to $.....$
  • $\sqrt{2}\left(\cos \frac{5 \pi}{12}+ i \sin \frac{5 \pi}{12}\right)$
  • B
    $\cos \frac{\pi}{12}- i \sin \frac{\pi}{12}$
  • C
    $\sqrt{2}\left(\cos \frac{\pi}{12}+ i \sin \frac{\pi}{12}\right)$
  • D
    $\sqrt{2} i \left(\cos \frac{5 \pi}{12}- i \sin \frac{5 \pi}{12}\right)$
Answer
Correct option: A.
$\sqrt{2}\left(\cos \frac{5 \pi}{12}+ i \sin \frac{5 \pi}{12}\right)$
a
$Z =\frac{ i -1}{\cos \frac{\pi}{3}+ i \sin \frac{\pi}{3}}=\frac{ i -1}{\frac{1}{2}+\frac{\sqrt{3}}{2} i }$

$=\frac{ i -1}{\frac{1}{2}+\frac{\sqrt{3}}{2} i } \times \frac{\frac{1}{2}-\sqrt{\frac{3}{2} i }}{\frac{1}{2}-\sqrt{3 / 2} i }=\frac{\sqrt{3}-1}{2}+\frac{\sqrt{3}+1}{2} i$

Apply polar form,

$r \cos \theta=\frac{\sqrt{3}-1}{2}r$

$\sin \theta=\frac{\sqrt{3}+1}{2}$

Now, $\tan \theta=\frac{\sqrt{3}+1}{\sqrt{3}-1}$

So, $\quad \theta=\frac{5 \pi}{12}$

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MCQ 1721 Mark
Let $z_1=2+3 i$ and $z_2=3+4 i$. The set $S =\left\{ z \in C :\left| z - z _1\right|^2-\left|z-z_2\right|^2=\left|z_1-z_2\right|^2\right\}$ represents a
  • straight line with sum of its intercepts on the coordinate axes equals $14$
  • B
    hyperbola with the length of the transverse axis $7$
  • C
    straight line with the sum of its intercepts on the coordinate axes equals $-18$
  • D
    hyperbola with eccentricity $2$
Answer
Correct option: A.
straight line with sum of its intercepts on the coordinate axes equals $14$
a
$\left((x-2)^2+(y-3)^2\right)-\left((x-3)^2-(y-4)^2\right)=1+1$

$\Rightarrow x + y =7$

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MCQ 1731 Mark
Let $z$ be a complex number such that $\left|\frac{z-2 i}{z+i}\right|=2, z \neq-i$. Then $z$ lies on the circle of radius $2$ and centre
  • A
    $(2,0)$
  • B
    $(0,0)$
  • C
    $(0,2)$
  • $(0,-2)$
Answer
Correct option: D.
$(0,-2)$
d
$( z -2 i )(\overline{ z }+2 i )=4( z + i )(\overline{ z }- i )$

$z \overline{ z }+4+2 i ( z -\overline{ z })=4( z \overline{ z }+1+ i (\overline{ z }- z ))$

$3 z \overline{ z }-6 i ( z -\overline{ z })=0$

$x ^2+ y ^2-2 i (2 iy )=0$

$x ^2+ y ^2+4 y =0$

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MCQ 1741 Mark
For all $z \in C$ on the curve $C _1:| z |=4$, let the locus of the point $z +\frac{1}{ z }$ be the curve $C _2$. Then
  • the curves $C_1$ and $C_2$ intersect at $4$ points
  • B
    the curves $C_1$ lies inside $C_2$
  • C
    the curves $C_1$ and $C_2$ intersect at $2$ points
  • D
    the curves $C_2$ lies inside $C_1$
Answer
Correct option: A.
the curves $C_1$ and $C_2$ intersect at $4$ points
a
Let $w = z +\frac{1}{ z }=4 e ^{ i \theta}+\frac{1}{4} e ^{- i \theta}$

$\Rightarrow w =\frac{17}{4} \cos \theta+ i \frac{15}{4} \sin \theta$

So locus of $w$ is ellipse $\frac{x^2}{\left(\frac{17}{4}\right)^2}+\frac{y^2}{\left(\frac{15}{4}\right)^2}=1$

Locus of $z$ is circle $x ^2+ y ^2=16$

So intersect at $4$ points

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MCQ 1751 Mark
If the center and radius of the circle $\left|\frac{z-2}{z-3}\right|=2$ are respectively $(\alpha, \beta)$ and $\gamma$, then $3(\alpha+\beta+\gamma)$ is equal to
  • A
    $11$
  • B
    $9$
  • C
    $10$
  • $12$
Answer
Correct option: D.
$12$
d
$\sqrt{(x-2)^2+y^2}=2 \sqrt{(x-3)^2+y^2}$

$=x^2+y^2-4 x+4=4 x^2+4 y^2-24 x+36$

$=3 x^2+3 y^2-20 x+32=0$

$=x^2+y^2-\frac{20}{3} x +\frac{32}{3}=0$

$=(\alpha, \beta)=\left(\frac{10}{3}, 0\right)$

$\gamma=\sqrt{\frac{100}{9}-\frac{32}{3}}=\sqrt{\frac{4}{9}}=\frac{2}{3}$

$3(\alpha, \beta, \gamma)=3\left(\frac{10}{3}+\frac{2}{3}\right)$

$=12$

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MCQ 1761 Mark
Let $a, b$ be two real numbers such that $a b < 0$. If the complex number $\frac{1+ ai }{ b + i }$ is of unit modulus and $a+i b$ lies on the circle $|z-1|=|2 z|$, then a possible value of $\frac{1+[ a ]}{4 b }$, where $[ t ]$ is greatest integer function, is :
  • $-\frac{1}{2}$
  • B
    $-1$
  • C
    $1$
  • D
    $\frac{1}{2}$
Answer
Correct option: A.
$-\frac{1}{2}$
a
$a b < 0\left|\frac{1+a i}{b+i}\right|=1$

$|1+a i l=| b+i l$

$a^2+1=b^2+1 \Rightarrow a=\pm b \Rightarrow b=-a \quad \text { as } a b < 0$

$(a, b) \text { lies on }| z -1|=|2 z |$

$la + ib -1 \mid=2 l a + ibl$

$( a -1)^2+ b ^2=4\left( a ^2+ b ^2\right)$

$( a -1)^2= a ^2=4\left(2 a ^2\right)$

$1-2 a =6 a ^2 \Rightarrow 6 a ^2+2 a -1=0$

$a =\frac{-2 \pm \sqrt{28}}{12}=\frac{-1 \pm \sqrt{7}}{6}$

$a =\frac{\sqrt{7}-1}{6}$ and $b =\frac{1-\sqrt{7}}{6}$

${[ a ]=0}$

$\therefore \frac{1+[ a ]}{4 b }=\frac{6}{4(1-\sqrt{7})}=-\left(\frac{1+\sqrt{7}}{4}\right.$

$\text { or }[ a ]=0$

Similarly it is not matching with $a =\frac{-1-\sqrt{7}}{6}$

No answer is matching.

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MCQ 1771 Mark
For $\alpha, \beta, z \in C$ and $\lambda>1$, if $\sqrt{\lambda-1}$ is the radius of the circle $|z-\alpha|^2+|z-\beta|^2=2 \lambda$, then $|\alpha-\beta|$ is equal to $.............$.
  • A
    $4$
  • B
    $6$
  • $2$
  • D
    $8$
Answer
Correct option: C.
$2$
c
For circle :

$\left|z-z_1\right|^2+\left|z-z_2\right|^2=\left|z_1-z_2\right|^2$

$r =\frac{\left|z_1-z_2\right|}{2}=\frac{|\alpha-\beta|}{2}=\sqrt{\lambda-1}$

$2 \lambda=|\alpha-\beta|^2$

$|\alpha-\beta|=2 \sqrt{\lambda-1}$

$|\alpha-\beta|^2=4 \lambda-4=2 \lambda$

$\lambda=2$

$\Rightarrow|\alpha-\beta|^2=4$

$|\alpha-\beta|=2$

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MCQ 1781 Mark
Let $w _1$ be the point obtained by the rotation of $z_1=5+4 i$ about the origin through a right angle in the anticlockwise direction, and $w_2$ be the point obtained by the rotation of $z_2=3+5 i$ about the origin through a right angle in the clockwise direction. Then the principal argument of $w _1- w _2$ is equal to $...........$.
  • A
    $-\pi+\tan ^{-1} \frac{33}{5}$
  • B
    $-\pi-\tan ^{-1} \frac{33}{5}$
  • C
    $-\pi+\tan ^{-1} \frac{8}{9}$
  • $\pi-\tan ^{-1} \frac{8}{9}$
Answer
Correct option: D.
$\pi-\tan ^{-1} \frac{8}{9}$
d
$W _1= z _{ i } i =(5+4 i ) i =-4+5 i$

$W _2= z _2(- i )=(3+5 i )(- i )=5-3 i$

$W _1- W _2=-9+8 i$

$\text { Principal argument }=\pi-\tan ^{-1}\left(\frac{8}{9}\right)$

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MCQ 1791 Mark
Let $\omega=z \bar{z}+k_1 z+k_2 i z+\lambda(1+i), k_1, k_2 \in R$. Let $\operatorname{Re}(\omega)=0$ be the circle $C$ of radius 1 in the first quadrant touching the line $y=1$ and the $y$-axis. If the curve $\operatorname{Im}(\omega)=0$ intersects $C$ at $A$ and $B$, then $30(A B)^2$ is equal to $.......$.
  • A
    $23$
  • B
    $22$
  • $24$
  • D
    $21$
Answer
Correct option: C.
$24$
c
$\omega=z \bar{z}+k_1 z+k_2 i z+\lambda(1+i)$

$\operatorname{Re}(w)=x^2+y^2+k_1 x-k_2 y+\lambda=0$

$\text { Centre } \equiv\left(\frac{-k_1}{2}, \frac{k_2}{2}\right) \equiv(1,2)$

$\Rightarrow k_1=-2, k_2=4$

$\text { radius }=1 \Rightarrow \lambda=4$

$\operatorname{Im}=k_1 y+k_2 x+\lambda=0$

$\therefore 2 x-y+2=0$

$d=\frac{2}{\sqrt{5}}$

$\frac{1^2}{4}=1-\frac{4}{5}=\frac{1}{5}$

$\therefore 301^2=24$

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MCQ 1801 Mark
Let $p , q \in R$ and $(1-\sqrt{3} i )^{200}=2^{199}( p + iq )$, $i =\sqrt{-1}$ Then $p + q + q ^2$ and $p - q + q ^2$ are roots of the equation.
  • A
    $x ^2+4 x -1=0$
  • $x^2-4 x+1=0$
  • C
    $x^2+4 x+1=0$
  • D
    $x ^2-4 x -1=0$
Answer
Correct option: B.
$x^2-4 x+1=0$
b
$(1-\sqrt{3} i )^{200}=2^{199}( p + iq )$

$2^{200}\left(\cos \frac{\pi}{3}- i \sin \frac{\pi}{3}\right)^{200}=2^{199}( p + iq )$ $2\left(-\frac{1}{2}- i \frac{\sqrt{3}}{2}\right)= p + iq$

$p =-1, q =-\sqrt{3}$

$\alpha= p + q + q ^2=2-\sqrt{3}$

$\beta= p - q + q ^2=2+\sqrt{3}$

$\alpha+\beta=4$

$\alpha \cdot \beta=1$

equation $x^2-4 x+1=0$

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MCQ 1811 Mark
The value of $\left(\frac{1+\sin \frac{2 \pi}{9}+i \cos \frac{2 \pi}{9}}{1+\sin \frac{2 \pi}{9}-i \cos \frac{2 \pi}{9}}\right)^3$ is
  • A
    $\frac{-1}{2}(1-i \sqrt{3})$
  • B
    $\frac{1}{2}(1-i \sqrt{3})$
  • $\frac{-1}{2}(\sqrt{3}-i)$
  • D
    $\frac{1}{2}(\sqrt{3}+i)$
Answer
Correct option: C.
$\frac{-1}{2}(\sqrt{3}-i)$
c
Let $\sin \frac{2 \pi}{9}+ i \cos \frac{2 \pi}{9}= z$

$\left(\frac{1+ z }{1+\bar{z}}\right)^3=\left(\frac{1+ z }{1+\frac{1}{ z }}\right)^3= z ^3$

$\Rightarrow\left( i \left(\cos \frac{2 \pi}{9}- i \sin \frac{2 \pi}{9}\right)\right)^3$

$=- i \left(\cos \frac{2 \pi}{3}- i \sin \frac{2 \pi}{3}\right)=- i \left(\frac{-1}{2}- i \frac{\sqrt{3}}{2}\right)$

$\Rightarrow \frac{-1}{2}(\sqrt{3}-i)$

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MCQ 1821 Mark
Let $\alpha, \beta$ be the roots of the quadratic equation $x^2+\sqrt{6} x+3=0$. Then $\frac{\alpha^{23}+\beta^{23}+\alpha^{14}+\beta^{14}}{\alpha^{15}+\beta^{15}+\alpha^{10}+\beta^{10}}$ is equal to 
  • A
    $729$
  • B
    $72$
  • $81$
  • D
    $9$
Answer
Correct option: C.
$81$
c
$\alpha, \beta=\frac{-\sqrt{6} \pm \sqrt{6-12}}{2}=\frac{-\sqrt{6} \pm \sqrt{6} i }{2}$

$=\sqrt{3} e ^{ \pm \frac{3 \pi i }{4}}$

Required expression

$=\frac{(\sqrt{3})^{23}\left(2 \cos \frac{69 \pi}{4}\right)+(\sqrt{3})^{14}\left(2 \cos \frac{42 \pi}{4}\right)}{(\sqrt{3})^{15}\left(2 \cos \frac{45 \pi}{4}\right)+(\sqrt{3})^{10}\left(2 \cos \frac{30 \pi}{4}\right)}$

$(\sqrt{3})^8=81$

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MCQ 1831 Mark
Let $\alpha, \beta$ be the roots of the equation $x^2-\sqrt{2} x+2=0$. Then $\alpha^{14}+\beta^{14}$ is equal to
  • A
    $-64 \sqrt{2}$
  • B
    $-128 \sqrt{2}$
  • C
    $-64$
  • $-128$
Answer
Correct option: D.
$-128$
d
$x^2-\sqrt{2} x+2=0$

$x=\frac{\sqrt{2} \pm \sqrt{2-8}}{2}=\frac{\sqrt{2} \pm \sqrt{6} i}{2}$

$\alpha=\frac{\sqrt{2}+\sqrt{6} i}{2}=\sqrt{2} e^{\frac{i \pi}{3}}$ $\beta=\sqrt{2} e^{\frac{-i \pi}{3}}$

$\alpha^{14}=2^7 e^{\frac{i 14 \pi}{3}}=128\left[e^{\frac{i 2 \pi}{3}}\right]$

$\beta^{14}=128\left[e^{\frac{-i 2 \pi}{3}}\right]$

$\alpha^{14}+\beta^{14}=128(2) \cos \left(\frac{2 \pi}{3}\right)=-128$

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MCQ 1841 Mark
Let $\quad S=\left\{z \in C-\{i, 2 i\}: \frac{z^2+8 i z-15}{z^2-3 i z-2} \in R \right\}$. $\alpha-\frac{13}{11} i \in S , \alpha \in R -\{0\}$, then $242 \alpha^2$ is equal to
  • $1680$
  • B
    $1681$
  • C
    $1682$
  • D
    $1683$
Answer
Correct option: A.
$1680$
a
$\left(\frac{z^2+81 z-15}{z^2-3 i z-2}\right) \in R$

$\Rightarrow 1+\frac{(11 i z-13)}{\left(z^2-3 i z-2\right)} \in R$

Put $z=\alpha-\frac{13}{11} i$

$\Rightarrow\left(z^2-3 i z-2\right)$ is imaginary

Put $z=x+i y$

$\Rightarrow\left(x^2-y^2+2 x y i-3 i x+3 y-2\right) \in \text { Imaginary }$

$\Rightarrow \operatorname{Re}\left(x^2-y^2+3 y-2+(2 x y-3 x) i\right)=0$

$\Rightarrow x^2-y^2+3 y-2=0$

$x^2=y^2-3 y+2$

$x^2=y^2-3 y+2$

$x^2=(y-1)(y-2) \therefore z=\alpha-\frac{13}{11} i$

Put $x=\alpha, y=\frac{-13}{11}$

$\alpha^2=\left(\frac{-13}{11}-1\right)\left(\frac{-13}{11}-2\right)$

$\alpha^2=\frac{(24 \times 35)}{121}$

$242 \alpha^2=48 \times 35=1680$

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MCQ 1851 Mark
Let $C$ be the circle in the complex plane with centre $z_0=\frac{1}{2}(1+3 i)$ and radius $r=1$. Let $z_1=1+$ $i$ and the complex number $z_2$ be outside the circle $C$ such that $\left|z_1-z_0\right|\left|z_2-z_0\right|=1$. If $z_0, z_1$ and $z_2$ are collinear, then the smaller value of $\left|z_2\right|^2$ is equal to $.............$. 
  • A
    $\frac{13}{2}$
  • $\frac{5}{2}$
  • C
    $\frac{3}{2}$
  • D
    $\frac{7}{2}$
Answer
Correct option: B.
$\frac{5}{2}$
b
$\left|z_1-z_0\right|=\left|\frac{1-i}{2}\right|=\frac{1}{\sqrt{2}}$

$\Rightarrow\left|z_2-z_{\circ}\right|=\sqrt{2} ; \text { centre }\left(\frac{1}{2}, \frac{3}{2}\right)$

$z_{0}\left(\frac{1}{2}, \frac{3}{2}\right) \text { and } z_1(1,1)$

$\tan \theta=-1 \Rightarrow \theta=135^{\circ}$

$z_2\left(\frac{1}{2}+\sqrt{2} \cos 135^{\circ}, \frac{3}{2}+\sqrt{2} \sin 135^{\circ}\right)$

or

$\left(\frac{1}{2}-\sqrt{2} \cos 135^{\circ}, \frac{3}{2}-\sqrt{2} \sin 135^{\circ}\right)$

$\Rightarrow z_2\left(-\frac{1}{2}, \frac{5}{2}\right) \text { or } z_2\left(\frac{3}{2}, \frac{1}{2}\right)$

$\Rightarrow\left|z_2\right|^2=\frac{26}{4}, \frac{5}{2}$

$\Rightarrow\left|z_2\right|_{\min }^2=\frac{5}{2}$

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MCQ 1861 Mark
Let $z _{1}$ and $z _{2}$ be two complex numbers such that $\overline{ z }_{1}=i \overline{ z }_{2}$ and $\arg \left(\frac{ z _{1}}{\overline{ z }_{2}}\right)=\pi$. Then
  • A
    $\arg z _{2}=\frac{\pi}{4}$
  • B
    $\arg z _{2}=-\frac{3 \pi}{4}$
  • $\arg z _{1}=\frac{\pi}{4}$
  • D
    $\arg z _{1}=-\frac{3 \pi}{4}$
Answer
Correct option: C.
$\arg z _{1}=\frac{\pi}{4}$
c
$\overline{ z }_{1}= i _{2}$

$z _{1}=- iz _{2}$

$\arg \left(\frac{ z _{1}}{\overline{ z }_{2}}\right)=\pi$

$\arg \left(- i \frac{ z _{2}}{\overline{ z }_{2}}\right)=\pi \quad \arg \left( z _{2}\right)=\theta$

$-\frac{\pi}{2}+\theta+\theta=\pi$

$2 \theta=\frac{3 \pi}{2}$

$\arg \left( z _{2}\right)=\theta=\frac{3 \pi}{4}, \arg z _{1}=\frac{\pi}{4}$

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MCQ 1871 Mark
If $z =2+3 i$, then $z ^{5}+(\overline{ z })^{5}$ is equal to.
  • $244$
  • B
    $224$
  • C
    $245$
  • D
    $265$
Answer
Correct option: A.
$244$
a
$z^{5}+(\bar{z})^{5}=(2+3 i)^{5}+(2-3 i)^{5}$

$=2\left({ }^{5} C_{0} 2^{5}+{ }^{5} C_{2} 2^{3}(3 i)^{2}+{ }^{5} C_{4} 2^{1}(3 i)^{4}\right)$

$=2(32+10 \times 8(-9)+5 \times 2 \times 81)=244$

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MCQ 1881 Mark
The number of points of intersection of $| z -(4+3 i )|=2$ and $| z |+| z -4|=6, z \in C$ is
  • A
    $0$
  • B
    $1$
  • $2$
  • D
    $3$
Answer
Correct option: C.
$2$
c
$C:(x-4)^{2}+(y-3)^{2}=4$

$E: \frac{(x-2)^{2}}{9}+\frac{y^{2}}{5}=1$

Lower Extremity of vertical diameter of circle $\rightarrow(4,1)$

Put in ellipse $\Rightarrow \frac{(4-2)^{2}}{9}+\frac{1}{5}-1$

$=\frac{4}{9}+\frac{1}{5}-1$

$=\frac{29}{45}-1<0$

Two Solutions

Answer (C)

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MCQ 1891 Mark
Let $\arg ( z )$ represent the principal argument of the complex number $z$. The, $| z |=3$ and $\arg ( z -1)-$ $\arg ( z +1)=\frac{\pi}{4}$ intersect
  • A
    Exactly at one point
  • B
    Exactly at two points
  • Nowhere
  • D
    At infinitely many points.
Answer
Correct option: C.
Nowhere
c

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MCQ 1901 Mark
For $z \in C$ if the minimum value of $(|z-3 \sqrt{2}|+|z-p \sqrt{2} i|)$ is $5 \sqrt{2}$, then a value of $P$ is $.......$
  • A
    $3$
  • B
    $\frac{7}{2}$
  • $4$
  • D
    $\frac{9}{2}$
Answer
Correct option: C.
$4$
c
It is sum of distance of $z$ from $(3 \sqrt{2}, 0)$ and $(0, p \sqrt{2})$

For minimising, $z$ should lie on $A B$ and $A B=5 \sqrt{2}$

$(A B)^{2}=18+2 p^{2}$

$p=\pm 4$

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MCQ 1911 Mark
Let $\alpha$ be a root of the equation $1+x^{2}+x^{4}=0$. Then the value of $\alpha^{1011}+\alpha^{\text {2022 }}-\alpha^{\text {3033}}$ is equal to
  • $1$
  • B
    $\alpha$
  • C
    $1+\alpha$
  • D
    $1+2 \alpha$
Answer
Correct option: A.
$1$
a
$x^{4}+x^{2}+1=0$

$\Rightarrow\left(x^{2}+x+1\right)\left(x^{2}-x+1\right)=0$

$\Rightarrow x=\pm \;\omega, \pm \;\omega^{2}$ where $\omega=1^{1 / 3}$ and imaginary.

So $\alpha^{1011}+\alpha^{2002}-\alpha^{3033}=1+1-1=1$

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MCQ 1921 Mark
Let $\alpha$ and $\beta$ be the roots of the equation $x^{2}+(2 i -$ $1)=0$. Then, the value of $\left|\alpha^{8}+\beta^{8}\right|$ is equal to
  • $50$
  • B
    $250$
  • C
    $1250$
  • D
    $1500$
Answer
Correct option: A.
$50$
a
$X^{2}=1-2 i \quad \Rightarrow \alpha^{2}=1-2 i , \quad \beta^{2}=1-2 i$

Hence $\alpha^{8}=\beta^{8}$

$\left|\alpha^{8}+\beta^{8}\right|=\left|2 \alpha^{8}\right|=2\left|\alpha^{2}\right|^{4}$

$=2 \sqrt{5}^{4}=50$

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MCQ 1931 Mark
Sum of squares of modulus of all the complex numbers $z$ satisfying $\bar{z}=i z^{2}+z^{2}-z$ is equal to
  • A
    $50$
  • $2$
  • C
    $29$
  • D
    $9$
Answer
Correct option: B.
$2$
b
$z +\overline{ z }=i z ^{2}+ z ^{2}$

Consider $z=x+i y$

$2 x=(i+1)\left(x^{2}-y^{2}+2 x y i\right)$

$\Rightarrow 2 x=x^{2}-y^{2}-2 x y \text { and } x^{2}-y^{2}+2 x y=0$

$\Rightarrow 2 x=-4 x y$

$\Rightarrow x=0 \text { or } y=\frac{-1}{2}$

Case $1: x=0 \Rightarrow y=0$ here $z=0$

$\text { Case } 2: y=\frac{-1}{2}$

$\Rightarrow 4 x^{2}-4 x-1=0$

$(2 x-1)^{2}=2$

$2 x-1=\pm \sqrt{2}$

$x=\frac{1 \pm \sqrt{2}}{2}$

Here $z =\frac{1+\sqrt{2}}{2}-\frac{ i }{2}$ or $z =\frac{1-\sqrt{2}}{2}-\frac{ i }{2}$

Sum of squares of modulus of $z$

$=0+\frac{(1+\sqrt{2})^{2}+1}{4}+\frac{(1-\sqrt{2})^{2}+1}{4}=\frac{8}{4}=2$

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MCQ 1941 Mark
Let $S_{1}=\left\{z_{1} \in C:\left|z_{1}-3\right|=\frac{1}{2}\right\}$ and $S_{2}=\left\{z_{2} \in C:\left|z_{2}-\right| z_{2}+1||=\left|z_{2}+\right| z_{2}-1||\right\} . \quad$ Then, for $z_{1} \in S_{1}$ and $z_{2} \in S_{2}$, the least value of $\left|z_{2}-z_{1}\right|$ is.
  • A
    $0$
  • B
    $\frac{1}{2}$
  • $\frac{3}{2}$
  • D
    $\frac{5}{2}$
Answer
Correct option: C.
$\frac{3}{2}$
c
$\left|z_{2}+\right| z_{2}-1||^{2}=\left|z_{2}-\right| z_{2}+1||^{2}$

$\left|z_{2}+\right| z_{2}-1||\left(\bar{z}_{2}+\left|z_{2}-1\right|\right)=\left(z_{2}-\left|z_{2}+1\right|\right)\left(\bar{z}_{2}-\left(z_{2}+1\right)\right)$

$z_{2}\left|\bar{z}_{2}+12_{2}-1\right|-\left(\bar{z}_{2}-\left|z_{2}+1\right|\right)+\bar{z}_{2}\left(\left|z_{2}-1\right|+\left|z_{2}+1\right|\right)$

$=\left|z_{2}+1\right|^{2}=\left|z_{2}-1\right|^{2}$

${\left[z_{2}+\bar{z}_{2}\right)\left(\left|z_{2}-1\right|\right)+\left(z_{2}+1 \mid\right)=2\left(z_{2}+\bar{z}_{2}\right) }$

$\left(z_{2}+\bar{z}_{2}\right)\left(\left|z_{2}-1\right|+\left|z_{2}+1\right|-2\right)=0$

$z_{2}+\bar{z}_{2}=0$ or $\left|z_{2}-1\right|+\left|z_{2}+1\right|-2=0$

$\therefore z_{2}+\bar{z}_{2}=0 \text { or }\left|z_{2}-1\right|+\left|z_{2}+1\right|-2=0$

$\therefore z _{2}$ lie on imaginary axis. Or on real axis with in $[-1,1]$

Also $\left|z_{1}-3\right|=\frac{1}{2}$ lie on circle having centre 3 and radius $\frac{1}{2}$

Clearly $\left|z_{1}-z_{2}\right| \min =\frac{5}{2}-1=\frac{3}{2}$

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MCQ 1951 Mark
If $z \neq 0$ be a complex number such that $\left| z -\frac{1}{ z }\right|=2$, then the maximum value of $|z|$ is.
  • A
    $\sqrt{2}$
  • B
    $1$
  • C
    $\sqrt{2}-1$
  • $\sqrt{2}+1$
Answer
Correct option: D.
$\sqrt{2}+1$
d
$| z -1 / z |=2$

|| $z \left|-\frac{1}{| z |}\right| \leq\left| z -\frac{1}{ z }\right| \leq| z |+\frac{1}{| z |}$

$\left| r -\frac{1}{ r }\right| \leq 2 \leq r +\frac{1}{ r }$

$\left| r -\frac{1}{ r }\right| \leq 2 \& r +\frac{1}{ r } \geq 2$ always true

$r -\frac{1}{ r } \geq-2 \& r -\frac{1}{ r } \leq 2$

$r ^{2}-1 \leq 2 r$

$r ^{2}-2 r \leq 1$

$( r -1)^{2} \leq 2$

$r -1 \leq \sqrt{2}$

$\left.\therefore z \right|_{\max }=1+\sqrt{2}$

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MCQ 1961 Mark
If $z = x + iy$ satisfies $|z|-2=0$ and $|z-i|-|z+5 i|=0$, then
  • A
    $x +2 y -4=0$
  • B
    $x^{2}+y-4=0$
  • $x^{2}+y-4=0$
  • D
    $x^{2}-y+3=0$
Answer
Correct option: C.
$x^{2}+y-4=0$
c
$|z-i|-|z+5 i|=0$

$|x+(y-1) i|=|x+(y+5) i|$

$x^{2}+(y-1)^{2}=x^{2}+(y+5)^{2}$

$(y-1)^{2}-(y+5)^{2}=0$

$(2 y+4)(-6)=0$

$y=-2$

$\therefore x^{2}+(-2)^{2}=4$

$x=0$

$Z \equiv(0,-2)$, check options

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MCQ 1971 Mark
Let $S=\left\{z \in C : z^{2}+\bar{z}=0\right\}$. Then $\sum \limits_{z \in S}(\operatorname{Re}(z)+\operatorname{Im}(z))$ is equal to$......$
  • A
    $1$
  • B
    $2$
  • C
    $3$
  • $0$
Answer
Correct option: D.
$0$
d
$S=\left\{z \in C: z^{2}+\bar{z}=0\right\}$

Let $z = x + iy$

$z ^{2}= x ^{2}- y ^{2}+2 ixy$

$\bar{z}=x-i y$

$z^{2}+\bar{z}=x^{2}-y^{2}+x+i(2 x y-y)=0$

$x^{2}+x-y^{2}=0 \text { \& } 2 x y-y=0$

$y=0$ or $x=\frac{1}{2}$

If $y =0 ; x =0,-1$

If $x=\frac{1}{2} ; y=\frac{\sqrt{3}}{2}, \frac{-\sqrt{3}}{2}$

$\sum_{z \in S}(\operatorname{Re}(z)+\operatorname{Im}(z)=\left(0-1+\frac{1}{2}+\frac{1}{2}\right)$

$+0+0+\frac{\sqrt{3}}{2}-\frac{\sqrt{3}}{2})$

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MCQ 1981 Mark
Let for some real numbers $\alpha$ and $\beta$, a $=\alpha-i \beta$. If the system of equations $4 ix +(1+ i ) y =0$ and $8\left(\cos \frac{2 \pi}{3}+i \sin \frac{2 \pi}{3}\right) x+\bar{a} y=0$ has more than one solution then $\frac{\alpha}{\beta}$ is equal to
  • A
    $-2+\sqrt{3}$
  • $2-\sqrt{3}$
  • C
    $2+\sqrt{3}$
  • D
    $-2-\sqrt{3}$
Answer
Correct option: B.
$2-\sqrt{3}$
b
$a =\alpha- i \beta ; \alpha \in R ; \beta \in R$

$4 ix +(1+ i ) y =0$ and

$8\left(\cos \frac{2 \pi}{3}+ i \sin \frac{2 \pi}{3}\right) x +\overline{ a } y =0$

$\left|\begin{array}{cc}4 i \quad 1+ i \\ 8 e ^{ i 2 \pi / 3} \quad \overline{ a }\end{array}\right|=0$

$\Rightarrow 4 i \overline{ a }-(1+ i ) 8 e ^{ i 2 \pi / 3}=0$

$\Rightarrow 4 i (\alpha+ i \beta)-8(1+ i )\left(\frac{-1+ i \sqrt{3}}{2}\right)=0$

$\Rightarrow i \alpha-\beta+1+\sqrt{3}+ i (1-\sqrt{3})=0$

$\Rightarrow \beta=\sqrt{3}+1$

$\alpha=\sqrt{3}-1$

So, $\frac{\alpha}{\beta}$

$\frac{\alpha}{\beta}=\frac{\sqrt{3}-1}{\sqrt{3}+1}=2-\sqrt{3}$

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MCQ 1991 Mark
Let $S=\{z \in C :|z-3| \leq 1$ and $z(4+3 i)+\bar{z}(4-3 i) \leq 24\}$.

If $\alpha+i \beta$ is the point in $S$ which is closest to $4 i$, then $25(\alpha+\beta)$ is equal to

  • A
    $40$
  • B
    $75$
  • $80$
  • D
    $85$
Answer
Correct option: C.
$80$
c
$|z-3| \leq 1$

represent pt. i/s circle of radius $1 $ centred at $(3,0)$

$z(4+3 i)+\bar{z}(4-3 i) \leq 24$

$(x+i y)(4+3 i)+(x-i y)(4-3 i) \leq 24$

$4 x+3 x i+4 i y-3 y+4 x-3 i x-4 i y-3 y \leq 24$

$8 x-6 y \leq 24$

$4 x-3 y \leq 12$

minimum of $(0,4)$ from circle $=\sqrt{3^{2}+4^{2}}-1=4$ will lie along line joining $(0,4) \&(3,0)$

$\therefore$ equation line

$\frac{x}{3}+\frac{y}{4}=1 \Rightarrow 4 x+3 y=12 \ldots \text { (i) }$

equation circle $(x-3)^{2}+y^{2}=1 \ldots$ $(ii)$

$\left(\frac{12-3 y}{4}-3\right)^{2}+y^{2}=1$

$\left(\frac{-3 y}{4}\right)^{2}+y^{2}=1$

$\frac{25 y^{2}}{16}=1 \Rightarrow y=\pm \frac{4}{5}$

for minimum distance $y=\frac{4}{5}$

$\therefore x=\frac{12}{5}$

$\therefore 25(\alpha+\beta)=25\left(\frac{4}{5}+\frac{12}{5}\right)$

$=16 \times 5=80$

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MCQ 2001 Mark
Let $A=\{z \in C: 1 \leq 1 z-(1+i) \leq 2\}$ and $B=\{z \in A:|z-(1-i)|=1\}$. Then, $B$ 
  • A
    is an empty set
  • B
    contains exactly two elements
  • C
    contains exactly three elements
  • is an infinite set
Answer
Correct option: D.
is an infinite set
d
$A=\{z \in C: 1 \leq z-(1+i) \leq 2\}$

$B=\{z \in A:|z-(1-i)|=1\}$

$A \cap B$ has infinite set

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