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Solve the Following Question.(4 Marks)

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22 questions · self-marked practice — reveal the answer and mark yourself.

Question 14 Marks
If $\alpha$ and $\beta$ are complex cube roots of unity, prove that $(1-\alpha)(1-\beta)\left(1-\alpha^2\right)\left(1-\beta^2\right)=9$.
Answer
α and β are the complex cube roots of unity.

$\begin{aligned} \therefore \quad \alpha & =\frac{-1+i \sqrt{3}}{2} \text { and } \beta=\frac{-1-i \sqrt{3}}{2} \\ \therefore \quad \alpha \beta & =\left(\frac{-1+i \sqrt{3}}{2}\right)\left(\frac{-1-i \sqrt{3}}{2}\right) \\ & =\frac{(-1)^2-(i \sqrt{3})^2}{4} \\ & =\frac{1-(-1)(3)}{4} \\ & =\frac{1+3}{4}\end{aligned}$

$\therefore \quad \alpha \beta=1$

Also, $\begin{aligned} \alpha+\beta & =\frac{-1+i \sqrt{3}}{2}+\frac{-1-i \sqrt{3}}{2} \\ & =\frac{-1+i \sqrt{3}-1-i \sqrt{3}}{2}=\frac{-2}{2}\end{aligned}$

$\begin{aligned} \therefore \quad & \alpha+\beta=-1 \\ \therefore \quad & (1-\alpha)(1-\beta)\left(1-\alpha^2\right)\left(1-\beta^2\right) \\ & =(1-\alpha)(1-\beta)(1-\alpha)(1+\alpha)(1-\beta)(1+\beta) \\ & =(1-\alpha)^2(1-\beta)^2(1+\alpha)(1+\beta) \\ & =[(1-\alpha)(1-\beta)]^2(1+\alpha)(1+\beta) \\ & =(1-\beta-\alpha+\alpha \beta)^2(1+\alpha+\beta+\alpha \beta) \\ & =[1-(\alpha+\beta)+\alpha \beta]^2[1+(\alpha+\beta)+\alpha \beta] \\ & =[1-(-1)+1]^2(1-1+1) \\ & =3^2(1)=9\end{aligned}$

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Question 24 Marks
Convert the complex numbers in polar form and also in exponential form.

$\frac{-3}{2}+\frac{3 \sqrt{3} i}{2}$

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Question 34 Marks
Convert the complex numbers in polar form and also in exponential form.

$z=\frac{2+6 \sqrt{3} i}{5+\sqrt{3} i}$

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Question 104 Marks
If α and β are the complex cube roots of unity, show that

1.$\alpha^2+\beta^2+\alpha \beta=0$

(ii) $\alpha^4+\beta^4+\alpha^{-1} \beta^{-1}=0$

2.If x = a + b, y = αa + βb and z = aβ + bα, where α and β are complex cube roots of unity,

show that $x y z=a^3+b^3$.

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Question 204 Marks
Find the values of x and y which satisfy the following equations (x, y ∈ R)

$\frac{x+i y}{2+3 i}+\frac{2+i}{2-3 i}=\frac{9}{13}(1+i)$

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Question 214 Marks
Find the values of x and y which satisfy the following equations (x, y ∈ R)

$\frac{x+1}{1+i}+\frac{y-1}{1-i}=i$

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