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Solve the Following Question.(3 Marks)

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

Question 33 Marks
Form the differential equation of:

the hyperbola whose length of transverse and conjugate axes are half of that of the

given hyperbola $\frac{x^2}{16}-\frac{y^2}{36}=k$.

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Question 43 Marks
Form the differential equation of:all parabolas which have 4b as latus rectum and whose axis is parallel to Y-axis.
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Question 53 Marks
Form the differential equation of:all circles which pass through the origin and whose centres lie on X-axis.
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Question 63 Marks
Obtain the differential equation by eliminating the arbitrary constants from the following equations:

$y=A e^{3 x+1}+B e^{-3 x+1}$

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Question 73 Marks
In each of the following examples verify that the given function is a solution of the differential equation.

$xy = ae ^{ x }+ be ^{- x }+ x ^2 ; x \frac{d^2 y}{d x^2}+2 \frac{d y}{d x}+x^2=x y+2$

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Question 83 Marks
Bacteria increase at the rate proporational to the number of bacteria present. If the original number $\mathrm{N}$ doubles in 3 hours, find in how many hours the number of bacteria will be $4 \mathrm{~N}$ ?
Answer
Let $x$ be the number of bacteria at time $t$. Since the rate of increase of $x$ is proporational $x$, the differential equation can be written as : $\frac{d x}{d t}=k x$
where $k$ is constant of proportionality.
Solving this differential equation we have $x=c_1 \cdot e^{k t}$, where $c_1=e^c$
Given that $x=\mathrm{N}$ when $t=0$
$\therefore \quad$ From equation (1) we get
$
\begin{aligned}
& \mathrm{N}=c_1 \cdot 1 \\
\therefore \quad & c_1=\mathrm{N} \\
\therefore \quad & x=\mathrm{N} \cdot e^{k t}
\end{aligned}
$
Again given that $x=2 \mathrm{~N}$ when $t=3$
$\therefore \quad$ From equation (2), we have
$
\begin{aligned}
& 2 \mathrm{~N}=\mathrm{N} \cdot e^{3 k} \\
& e^{3 k}=2
\end{aligned}
$
Now we have to find $t$, when $x=4 \mathrm{~N}$
$\therefore \quad$ From equation (2), we have
$
4 \mathrm{~N}=\mathrm{N} \cdot e^{k t}
$
i.e. $4=e^{k t}=\left(e^{3 k}\right)^{\frac{t}{3}}$
$
\begin{aligned}
& \therefore \quad 2^2=2^{\frac{t}{3}} \\
& \therefore \quad \frac{t}{3}=2 \\
& \therefore \quad t=6
\end{aligned}
$
by eq. (3)
Therefore, the number of bacteria will be $4 \mathrm{~N}$ in 6 hours.
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Question 93 Marks
The population of a town increasing at a rate proportional to the population at that time. If the population increases from 40 thousands to 60 thousands in 40 years, what will be the population in another 20 years.
$\text { (Given } \sqrt{\frac{3}{2}}=1 \cdot 2247 \text { ). }$
Answer
Let $P$ be the population at time t. Since rate of increase of $P$ is a proportional to $P$ itself, we have,
$
\frac{d P}{d t}=k \cdot P
$
where $k$ is constant of proportionality.
Solving this differential equation, we get
$P=a \cdot e^{k t}$, where $a=e^c \ldots(2)$
Initially $P=40,000$ when $t=0$
$\therefore \quad$ From equation (2), we have
$40,000=a \cdot 1 \quad \therefore a=40,000$
eq. (2) becomes
$
\therefore \quad P=40,000 \cdot e^{k t}
$
Again given that $P=60,000$ when $t=40$
$\therefore \quad$ From equation (3),
$60,000=40,000 \cdot e^{40 k}$
$e^{40 k}=\frac{3}{2}$
Now we have to find $P$ when $t=40+20$
$
=60 \text { years }
$
$\therefore \quad$ From equation (3), we have
$
\begin{aligned}
P & =40,000 \cdot e^{60 k}=40,000\left(e^{40 k}\right)^{\frac{3}{2}} \\
& =40,000\left(\frac{3}{2}\right)^{\frac{3}{2}}=73482
\end{aligned}
$
$\therefore \quad$ Required population will be 73482 .
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Question 133 Marks
Reduce each of the following differential equations to the separted variable form and hence find the general solution.$\frac{d y}{d x}=(4 x+y+1)^2$
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Question 143 Marks
Find the general solution of the following differential equations: $\frac{d y}{d x}=x \sqrt{25-x^2}$
Answer
$
\begin{aligned}
& \text {} \frac{d y}{d x}=x \sqrt{25-x^2} \\
& \therefore \quad d y=x \sqrt{25-x^2} \cdot d x
\end{aligned}
$
Integrating both sides, we get
$
\int d y=\int \sqrt{25-x^2} \cdot x \cdot d x
$
Put $25-x^2=t$
$
\begin{aligned}
& \therefore \quad-2 x \cdot d x=d t \\
& \therefore \quad x \cdot d x=-\frac{d t}{2}
\end{aligned}
$
Eq. (I) becomes, $\int d y=\int \sqrt{t}\left(-\frac{d t}{2}\right)$
$
\begin{aligned}
& \therefore \quad 2 \int d y=-\int \sqrt{t} \cdot d t \\
& \therefore \quad 2 \int d y+\int t^{\frac{1}{2}} \cdot d t=0 \\
& \therefore \quad 2 y+\frac{t^{\frac{3}{2}}}{\frac{3}{2}}=c_1 \\
& \therefore \quad 2 y+\frac{2}{3} t^{\frac{3}{2}}=c_1 \\
& \therefore \quad 6 y+2 t^{\frac{3}{2}}=3 c_1 \\
& \therefore \quad 6 y+2\left(25-x^2\right)^{\frac{3}{2}}=c
\end{aligned}
$
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Question 153 Marks
Obtain the differential euqation by eliminating the arbitrary constants from the following :
$y=c_1 e^{3 x}+c_2 e^{2 x}$
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Question 163 Marks
Find the equation of the curve passing through the point $\left(\frac{3}{\sqrt{2}}, \sqrt{2}\right)$ having slope of the

tangent to the curve at any point $(x, y)$ is $-\frac{4 x}{9 y}$.

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Question 263 Marks
Solve the following differential equations:

$x \sin \left(\frac{y}{x}\right) d y=\left[y \sin \left(\frac{y}{x}\right)-x\right] d x$

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Question 273 Marks
Reduce each of the following differential equations to the variable separable form and hence solve:(2x – 2y + 3) dx – (x – y + 1) dy = 0, when x = 0, y = 1
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Question 283 Marks
Reduce each of the following differential equations to the variable separable form and hence solve:

$(x-y)^2 \frac{d y}{d x}=a^2$

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Question 293 Marks
Reduce each of the following differential equations to the variable separable form and hence solve:

$\frac{d y}{d x}=\cos ( x + y )$

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Question 303 Marks
For each of the following differential equations, find the particular solution satisfying the given condition:

$(x+1) \frac{d y}{d x}-1=2 e^{-y}, y=0$, when $x=1$

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Question 313 Marks
For each of the following differential equations, find the particular solution satisfying the given condition:

$y (1+\log x ) \frac{d x}{d y}- x \log x =0, y = e ^2$, when $x = e$

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Question 323 Marks
For each of the following differential equations, find the particular solution satisfying the given condition:

$\left(x-y^2 x\right) d x-\left(y+x^2 y\right) d y=0$, when $x=2, y=0$

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Question 343 Marks
In each of the following examples verify that the given expression is a solution of the corresponding differential equation.

$y=\left(\sin ^{-1} x\right)^2+c_{;}\left(1-x^2\right) \frac{d^2 y}{d x^2}-x \frac{d y}{d x}=2$

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Question 363 Marks
Find the differential equation all parabolas having length of latus rectum 4a and axis is parallel to the X-axis.
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Question 373 Marks
Obtain the differential equation by eliminating the arbitrary constants from the following equations:

$y=e^{-2 x}(A \cos x+B \sin x)$

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Question 383 Marks
Obtain the differential equation by eliminating the arbitrary constants from the following equations:

$c_1 x^3+c_2 y^2=5$

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Question 393 Marks
Obtain the differential equation by eliminating the arbitrary constants from the following equations:

$y=c_1 e^{2 x}+c_2 e^{5 x}$

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