NCERT Solutions for Miscellaneous Exercise Chapter 9 Class 12 - Differential Equations

NCERT Solutions for Miscellaneous Exercise Chapter 9 Class 12 - Differential Equations

Komal MiglaniUpdated on 08 May 2025, 02:22 PM IST

Differential equations find their applications in the explanation of many real-life phenomena involving temporal change of quantities. For instance, city population growth typically exhibits a model with the growth rate proportional to the current population; this process can be explained using a straightforward exponential differential equation. In the same way, a balloon inflation with gas filled depends on pressures and temperatures, and the process can be explained with differential equations formulated from gas laws.

Created according to the latest CBSE 2025-26 syllabus, the NCERT Solutions for Class 12 Maths Chapter 9 Miscellaneous Exercise are created by subject experts at Careers360. The solutions give detailed, step-by-step solutions to help students better understand even complicated problems.

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  1. Differential Equations Class 12 Chapter 9 -Miscellaneous Exercise
  2. Topics covered in Chapter 9 Differential Equations: Miscellaneous Exercise
  3. NCERT Solutions Subject Wise
  4. Subject Wise NCERT Exemplar Solutions

Differential Equations Class 12 Chapter 9 -Miscellaneous Exercise

Question 1: Indicate Order and Degree.

(i) $\frac{d^2y}{dx^2} + 5x \left (\frac{dy}{dx} \right )^2-6y = \log x$

Answer:

Given function is
$\frac{d^2y}{dx^2} + 5x \left (\frac{dy}{dx} \right )^2-6y = \log x$
We can rewrite it as
$y''+5x(y')^2-6y = \log x$
Now, it is clear from the above that, the highest order derivative present in differential equation is $y''$

Therefore, the order of the given differential equation $\frac{d^2y}{dx^2} + 5x \left (\frac{dy}{dx} \right )^2-6y = \log x$ is 2
Now, the given differential equation is a polynomial equation in its derivative y '' and y 'and power raised to y '' is 1
Therefore, it's degree is 1

Question 1: Indicate Order and Degree.

(ii) $\left(\frac{dy}{dx} \right )^3 - 4\left(\frac{dy}{dx} \right )^2 + 7y = \sin x$

Answer:

Given function is
$\left(\frac{dy}{dx} \right )^3 - 4\left(\frac{dy}{dx} \right )^2 + 7y = \sin x$
We can rewrite it as
$(y')^3-4(y')^2+7y=\sin x$
Now, it is clear from the above that, the highest order derivative present in differential equation is y'

Therefore, order of given differential equation is 1
Now, the given differential equation is a polynomial equation in it's dervatives y 'and power raised to y ' is 3
Therefore, it's degree is 3

Question 1: Indicate Order and Degree.

(iii) $\frac{d^4 y}{dx^4} - \sin\left(\frac{d^3y}{dx^3} \right ) = 0$

Answer:

Given function is
$\frac{d^4 y}{dx^4} - \sin\left(\frac{d^3y}{dx^3} \right ) = 0$
We can rewrite it as
$y''''-\sin y''' = 0$
Now, it is clear from the above that, the highest order derivative present in differential equation is y''''

Therefore, order of given differential equation is 4
Now, the given differential equation is not a polynomial equation in it's dervatives
Therefore, it's degree is not defined

Question 2: Verify that the given function (implicit or explicit) is a solution of the corresponding differential equation.

(i) $xy = ae^x + be^{-x} + x^2\qquad :\ x\frac{d^2y}{dx^2} + 2\frac{dy}{dx} - xy +x^2 -2 =0$

Answer:

Given,

$xy = ae^x + be^{-x} + x^2$

Now, differentiating both sides w.r.t. x,

$x\frac{dy}{dx} + y = ae^x - be^{-x} + 2x$

Again, differentiating both sides w.r.t. x,

$\\ (x\frac{d^2y}{dx^2} + \frac{dy}{dx}) + \frac{dy}{dx} = ae^x + be^{-x} + 2 \\ $

$\implies x\frac{d^2y}{dx^2} + 2\frac{dy}{dx} = ae^x + be^{-x} + 2 \\ $

$\implies x\frac{d^2y}{dx^2} + 2\frac{dy}{dx} = xy -x^2 + 2 \\$

$\implies x\frac{d^2y}{dx^2} + 2\frac{dy}{dx} - xy + x^2 + 2$

Therefore, the given function is the solution of the corresponding differential equation.

Question 2: Verify that the given function (implicit or explicit) is a solution of the corresponding differential equation.

(ii) $y = e^x(a\cos x + b \sin x )\qquad : \ \frac{d^2y}{dx^2} - 2\frac{dy}{dx} + 2y = 0$

Answer:

Given,

$y = e^x(a\cos x + b \sin x )$

Now, differentiating both sides w.r.t. x,

$\frac{dy}{dx} = e^x(-a\sin x + b \cos x ) + e^x(a\cos x + b \sin x ) =e^x(-a\sin x + b \cos x ) +y$

Again, differentiating both sides w.r.t. x,

$\\ \frac{d^2y}{dx^2} = e^x(-a\cos x - b \sin x ) + e^x(-a\sin x + b \cos x ) + \frac{dy}{dx} \\$

$= -y + (\frac{dy}{dx} -y) + \frac{dy}{dx} \\$

$\implies \frac{d^2y}{dx^2} - 2\frac{dy}{dx} + 2y = 0$

Therefore, the given function is the solution of the corresponding differential equation.

Question 2 Verify that the given function (implicit or explicit) is a solution of the corresponding differential equation.

(iii) $y= x\sin 3x \qquad : \ \frac{d^2y}{dx^2} + 9y - 6\cos 3x = 0$

Answer:

Given,

$y= x\sin 3x$

Now, differentiating both sides w.r.t. x,

$y= x\sin 3x \frac{dy}{dx} = x(3\cos 3x) + \sin 3x$

Again, differentiating both sides w.r.t. x,

$\\ \frac{d^2y}{dx^2} = 3x(-3\sin 3x) + 3\cos 3x + 3\cos 3x \\ $

$= -9y + 6\cos 3x \\$

$\implies \frac{d^2y}{dx^2} + 9y - 6\cos 3x = 0$

Therefore, the given function is the solution of the corresponding differential equation.

Question 2: Verify that the given function (implicit or explicit) is a solution of the corresponding differential equation.

(iv) $x^2 = 2y^2\log y\qquad : \ (x^2 + y^2)\frac{dy}{dx} - xy = 0$

Answer:

Given,

$x^2 = 2y^2\log y$

Now, differentiating both sides w.r.t. x,

$\\ 2x = (2y^2.\frac{1}{y} + 2(2y)\log y)\frac{dy}{dx} = 2(y + 2y\log y)\frac{dy}{dx} \\$

$\implies \frac{dy}{dx} = \frac{x}{y(1+ 2\log y)}$

Putting $\frac{dy}{dx}\ and \ x^2$ values in LHS

$\\ (2y^2\log y + y^2)\frac{dy}{dx} - xy = y^2(2\log y + 1)\frac{x}{y(1+ 2\log y)} -xy \\$

$= xy - xy = 0 = RHS$

Therefore, the given function is the solution of the corresponding differential equation.

Question 3: Form the differential equation representing the family of curves given by $(x-a)^2 + 2y^2 = a^2$ , where a is an arbitrary constant.

Answer:

Given equation is
$(x-a)^2 + 2y^2 = a^2$
we can rewrite it as
$2y^2 = a^2-(x-a)^2$ -(i)
Differentiate both the sides w.r.t x
$\frac{d\left ( 2y^2 \right )}{dx}=\frac{d(a^2-(x-a)^2)}{dx}$
$4yy^{'}=4y\frac{dy}{dx}=-2(x-a)\\ \\$
$(x-a)= -2yy'\Rightarrow a = x+2yy'$ -(ii)
Put value from equation (ii) in (i)
$(-2yy')^2+2y^2= (x+2yy')^2\\$

$4y^2(y')^2+2y^2= x^2+4y^2(y')^2+4xyy'\\$

y' = \frac{2y^2-x^2}{4xy}$
Therefore, the required differential equation is $y' = \frac{2y^2-x^2}{4xy}$

Question 4: Prove that $x^2 - y^2 = c (x^2 + y^2 )^2$ is the general solution of differential equation $(x^3 - 3x y^2 ) dx = (y^3 - 3x^2 y) dy$ , where c is a parameter.

Answer:

Given,

$
\begin{aligned}
& \left(x^3-3 x y^2\right) d x=\left(y^3-3 x^2 y\right) d y \\
& \Longrightarrow \frac{d y}{d x}=\frac{\left(x^3-3 x y^2\right)}{\left(y^3-3 x^2 y\right)}
\end{aligned}
$


Now, let $\mathbf{y}=\mathrm{vx}$

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


Substituting the values of $y$ and $y^{\prime}$ in the equation,

$
\begin{aligned}
& v+x \frac{d v}{d x}=\frac{\left(x^3-3 x(v x)^2\right)}{\left((v x)^3-3 x^2(v x)\right)} \\
& \Longrightarrow v+x \frac{d v}{d x}=\frac{1-3 v^2}{v^3-3 v} \\
& \Longrightarrow x \frac{d v}{d x}=\frac{1-3 v^2}{v^3-3 v}-v=\frac{1-v^4}{v^3-3 v} \\
& \Longrightarrow\left(\frac{v^3-3 v}{1-v^4}\right) d v=\frac{d x}{x}
\end{aligned}
$


Integrating both sides we get,

$
\int\left(\frac{v^3-3 v}{1-3 v^4}\right) d v=\log x+\log C^{\prime}
$


Now, $\int\left(\frac{v^3-3 v}{1-3 v^4}\right) d v=\int \frac{v^3}{1-v^4} d v-3 \int \frac{v d v}{1-v^4}$

$
\Rightarrow \int\left(\frac{v^3-3 v}{1-3 v^4}\right) d v=I_1-3 I_2 \text {, where } I_1=\int \frac{v^3}{1-v^4} d v \text { and } I_2=\int \frac{v d v}{1-v^4}
$


Let $1-v^4=\mathrm{t}$

$
\begin{aligned}
& \frac{d}{d v}\left(1-v^4\right)=\frac{d t}{d v} \\
& \Longrightarrow-4 v^3=\frac{d t}{d v} \\
& \Longrightarrow v^3 d v=-\frac{d t}{4}
\end{aligned}
$

Now,

$
\mathrm{I}_1=\int-\frac{\mathrm{dt}}{4}=-\frac{1}{4} \log \mathrm{t}=-\frac{1}{4} \log \left(1-\mathrm{v}^4\right)
$

and

$
I_2=\int \frac{v d v}{1-v^4}=\int \frac{v d v}{1-\left(v^2\right)^2}
$


Let $v^2=p$

$
\begin{aligned}
& \Rightarrow \frac{d}{d v}\left(v^2\right)=\frac{d p}{d v} \\
& \Rightarrow 2 v=\frac{d p}{d v}
\end{aligned}
$


$
\Rightarrow \mathrm{vdv}=\frac{\mathrm{dp}}{2}
$


$
\therefore \mathrm{I}_2=\frac{1}{2} \int \frac{\mathrm{dp}}{1-\mathrm{p}^2}=\frac{1}{2 \times 2} \log \left|\frac{1+\mathrm{p}}{1-\mathrm{p}}\right|=\frac{1}{4}\left|\frac{1+\mathrm{v}^2}{1-\mathrm{v}}\right|
$


Now, substituting the values of $\mathrm{I}_1$ and $\mathrm{I}_2$ in the above equation, we get,

$
\int\left(\frac{\mathrm{v}^3-3 \mathrm{y}}{1-\mathrm{v}^4}\right) \mathrm{dv}=-\frac{1}{4} \log \left(1-\mathrm{v}^4\right)-\frac{3}{4} \log \left|\frac{1+\mathrm{v}^2}{1-\mathrm{v}^2}\right|
$


Thus,

$
\begin{aligned}
& -\frac{1}{4} \log \left(1-\mathrm{v}^4\right)-\frac{3}{4} \log \left|\frac{1+\mathrm{v}^2}{1-\mathrm{v}^2}\right|=\log \mathrm{x}+\log \mathrm{C}^{\prime} \\
& \Rightarrow-\frac{1}{4} \log \left[\left(1-\mathrm{v}^4\right)\left(\frac{1+\mathrm{v}^2}{1-\mathrm{v}^2}\right)^3\right]=\log \mathrm{C}^{\prime} \mathrm{x} \\
& \Rightarrow \frac{\left(1+\mathrm{v}^2\right)^4}{\left(1-\mathrm{v}^2\right)^2}=\left(\mathrm{C}^{\prime} \mathrm{x}\right)^{-4} \\
& \Rightarrow \frac{\left(1+\frac{y^2}{x^2}\right)^4}{\left(1-\frac{y^2}{x^2}\right)^2}=\frac{1}{\mathrm{C}^4 \mathrm{x}^4} \\
& \left(x^2-y^2\right)^2=C^{\prime 4}\left(x^2+y^2\right)^4 \\
& \Longrightarrow\left(x^2-y^2\right)=C^{\prime 2}\left(x^2+y^2\right)^2 \\
& \Longrightarrow\left(x^2-y^2\right)=K\left(x^2+y^2\right)^2, \text { where } K=C^{\prime 2}
\end{aligned}
$

Question 5: Form the differential equation of the family of circles in the first quadrant which touch the coordinate axes.

Answer:

1654780046916

Now, equation of the circle with center at (x,y) and radius r is
$(x-a)^2+(y-b)^2 = r^2$
Since, it touch the coordinate axes in first quadrant
Therefore, x = y = r
$(x-a)^2+(y-a)^2 = a^2$ -(i)
Differentiate it w.r.t x
we will get
$2(x-a)+2(y-a)y'= 0\\ $

$\\ 2x-2a+2yy'-2ay' = 0\\$

$a=\frac{x+yy'}{1+y'}$ -(ii)
Put value from equation (ii) in equation (i)
$(x-\frac{x+yy'}{1+y'})^2+(y-\frac{x+yy'}{1+y'})^2=\left ( \frac{x+yy'}{1+y'} \right )^2\\$

$\\ (x+xy'-x-yy')^2+(y+yy'-x-yy')^2=(x+yy')^2\\ $

$\\ (y')^2(x-y)^2+(x-y)^2=(x+yy')^2\\$

$\\ (x-y)^2\left ( (y')^2+1 \right )=(x+yy')^2$
Therefore, the differential equation of the family of circles in the first quadrant which touches the coordinate axes is $(x-y)^2\left ( (y')^2+1 \right )=(x+yy')^2$

Question 6: Find the general solution of the differential equation $\frac{dy}{dx} + \sqrt{\frac{1 - y^2}{1-x^2}} = 0$

Answer:

Given equation is
$\frac{dy}{dx} + \sqrt{\frac{1 - y^2}{1-x^2}} = 0$
we can rewrite it as
$\frac{dy}{dx } =- \sqrt{\frac{1-y^2}{1-x^2}}\\$

$\\ \frac{dy}{\sqrt{1-y^2}}= \frac{-dx}{\sqrt{1-x^2}}$
Now, integrate on both the sides
$\sin^{-1}y + C =- \sin ^{-1}x + C'\\ $

$\\ \sin^{-1}y+\sin^{-1}x= C$
Therefore, the general solution of the differential equation $\frac{dy}{dx} + \sqrt{\frac{1 - y^2}{1-x^2}} = 0$ is $\sin^{-1}y+\sin^{-1}x= C$

Question 7: Show that the general solution of the differential equation $\frac{dy}{dx} + \frac{y^2 + y + 1}{x^2 + x + 1} = 0$ is given by $(x + y + 1) = A (1 - x - y - 2xy)$ , where A is parameter.

Answer:

Given,

$
\begin{aligned}
& \frac{d y}{d x}+\frac{y^2+y+1}{x^2+x+1}=0 \\
& \Rightarrow \frac{\mathrm{dy}}{\mathrm{dx}}=-\left(\frac{\mathrm{y}^2+\mathrm{y}+1}{\mathrm{x}^2+\mathrm{x}+1}\right) \\
& \Rightarrow \frac{\mathrm{dy}}{\mathrm{y}^2+\mathrm{y}+1}=\frac{-\mathrm{dx}}{\mathrm{x}^2 \mathrm{dx}+1} \\
& \Rightarrow \frac{\mathrm{dy}}{\mathrm{y}^2+\mathrm{y}+1}+\frac{\mathrm{dx}}{\mathrm{x}^2+\mathrm{x}+1}=0
\end{aligned}
$


Integrating both sides,

$
\begin{aligned}
& \int \frac{d y}{y^2+y+1}+\int \frac{d x}{x^2+x+1}=C \\
& \Rightarrow \int \frac{d y}{\left(y+\frac{1}{2}\right)^2+\left(\frac{\sqrt{3}}{2}\right)^2}+\int \frac{d y}{\left(x+\frac{1}{2}\right)^2+\left(\frac{\sqrt{3}}{2}\right)^2}=C \\
& \Rightarrow \frac{2}{\sqrt{3}} \tan ^{-1}\left[\frac{\mathrm{y}+\frac{1}{2}}{\frac{\sqrt{3}}{2}}\right]+\frac{2}{\sqrt{3}} \tan ^{-1}\left[\frac{x+\frac{1}{2}}{\frac{\sqrt{3}}{2}}\right]=C \\
& \Rightarrow \tan ^{-1}\left[\frac{2 y+1}{\sqrt{3}}\right]+\tan ^{-1}\left[\frac{2 x+1}{\sqrt{3}}\right]=\mathrm{C} \Rightarrow \tan ^{-1}\left[\frac{\frac{2 y+1}{\sqrt{3}}+\frac{2 x+1}{\sqrt{3}}}{1-\frac{2 y+1}{\sqrt{3}} \cdot \frac{2 x+1}{\sqrt{3}}}\right]=\frac{\sqrt{3}}{2} C \\
& \Rightarrow \tan ^{-1}\left[\frac{\frac{2 x+2 y+2}{\sqrt[3]{3}}}{1-\left(\frac{4 x y+2 x+2 y+1}{3}\right)}\right]=\frac{\sqrt{3}}{2} C \\
& \Rightarrow \tan ^{-1}\left[\frac{2 \sqrt{3}(x+y+1)}{3-4 x y-2 x-2 y-1}\right]=\frac{\sqrt{3}}{2} C \\
& \Rightarrow \tan ^{-1}\left[\frac{2 \sqrt{3}(x+y+1)}{2(1-x-y-2 x y)}\right]=\frac{\sqrt{3}}{2} C \\
& \Rightarrow \frac{\sqrt{3}(x+y+1)}{(1-x-y-2 x y)}=\tan \left(\frac{\sqrt{3}}{2} c\right)
\end{aligned}
$


Let $\tan \left(\frac{\sqrt{3}}{2} c\right)=B$

$
x+y+1=\frac{2 B}{\sqrt{3}}(1-x-y-2 x y)
$


Let $A=\frac{2 B}{\sqrt{3}}$,

$
x+y+1=A(1-x-y-2 x y)
$


Hence proved.

Question 8: Find the equation of the curve passing through the point $\left(0,\frac{\pi}{4} \right )$ whose differential equation is $\sin x \cos y dx + \cos x \sin y dy = 0.$

Answer:

Given equation is
$\sin x \cos y dx + \cos x \sin y dy = 0.$
we can rewrite it as
$\frac{dy}{dx}= -\tan x\cot y\\$

$\\ \frac{dy}{\cot y}= -\tan xdx\\$

$\\ \tan y dy =- \tan x dx$
Integrate both the sides
$\log |\sec y|+C' = -\log|sec x|- C''\\ $

$\\ \log|\sec y | +\log|\sec x| = C\\$

$\\ \sec y .\sec x = e^{C}$
Now by using boundary conditiond, we will find the value of C
It is given that the curve passing through the point $\left(0,\frac{\pi}{4} \right )$
So,
$\sec \frac{\pi}{4} .\sec 0 = e^{C}\\ $

$\\ \sqrt2.1= e^C\\$

$\\ C = \log \sqrt2$
Now,
$\sec y.\sec x= e^{\log \sqrt 2}\\$

$\\ \frac{\sec x}{\cos y} = \sqrt 2\\ $

$\\ \cos y = \frac{\sec x}{\sqrt 2}$
Therefore, the equation of the curve passing through the point $\left(0,\frac{\pi}{4} \right )$ whose differential equation is $\sin x \cos y dx + \cos x \sin y dy = 0.$ is $\cos y = \frac{\sec x}{\sqrt 2}$

Question 9: Find the particular solution of the differential equation $(1 + e^ {2x} ) dy + (1 + y^2 ) e^x dx = 0$ , given that $y = 1$ when $x = 0$ .

Answer:

Given equation is
$(1 + e^ {2x} ) dy + (1 + y^2 ) e^x dx = 0$
we can rewrite it as
$\frac{dy}{dx}= -\frac{(1+y^2)e^x}{(1+e^{2x})}\\ $

$\\ \frac{dy}{1+y^2}= \frac{-e^xdx}{1+e^{2x}}$
Now, integrate both the sides
$\tan^{-1}y + C' =\int \frac{-e^{x}dx}{1+e^{2x}}$
$\int \frac{-e^{x}dx}{1+e^{2x}}\\$
Put
$e^x = t \\$

$e^xdx = dt$
$\int \frac{dt}{1+t^2}= \tan^{-1}t + C''$
Put $t = e^x$ again
$\int \frac{-e^{x}dx}{1+e^{2x}} = -\tan ^{-1}e^x+C''$
Put this in our equation
$\tan^{-1}y = -\tan ^{-1}e^x+C\\$

$\tan^{-1}y +\tan ^{-1}e^x=C$
Now, by using boundary conditions we will find the value of C
It is given that
y = 1 when x = 0
$\\ \tan^{-1}1 +\tan ^{-1}e^0=C\\ $

$\\ \frac{\pi}{4}+\frac{\pi}{4}= C\\$

$C = \frac{\pi}{2}$
Now, put the value of C

$\tan^{-1}y +\tan ^{-1}e^x=\frac{\pi}{2}$
Therefore, the particular solution of the differential equation $(1 + e^ {2x} ) dy + (1 + y^2 ) e^x dx = 0$ is $\tan^{-1}y +\tan ^{-1}e^x=\frac{\pi}{2}$

Answer:

Given,

$ye^\frac{x}{y}dx = (xe^\frac{x}{y} + y^2)dy$

$\\ ye^\frac{x}{y}\frac{dx}{dy} = xe^\frac{x}{y} + y^2 \\$

$\implies e^\frac{x}{y}[y\frac{dx}{dy} -x] = y^2 \\$

$\implies \frac{e^\frac{x}{y}[y\frac{dx}{dy} -x]}{y^2} = 1$

Let $\large e^\frac{x}{y} = t$

Differentiating it w.r.t. y, we get,

$\\ \frac{d}{dy}e^\frac{x}{y} = \frac{dt}{dy} \\$
$ \implies e^\frac{x}{y}.\frac{d}{dy}(\frac{x}{y}) = \frac{dt}{dy} \\$

$\implies \frac{e^\frac{x}{y}[y\frac{dx}{dy} -x]}{y^2} =\frac{dt}{dy}$

Thus from these two equations,we get,

$\\ \frac{dt}{dy} = 1 \\ $

$\implies \int dt = \int dy \\ $

$\implies t = y + C$

$\Longrightarrow e^{\frac{x}{y}}=y+C$

Question 11: Find a particular solution of the differential equation $(x - y) (dx + dy) = dx - dy,$ , given that $y = -1$ , when $x = 0$ . (Hint: put $x - y = t$ )

Answer:

Given equation is
$(x - y) (dx + dy) = dx - dy,$
Now, integrate both the sides
Put
$(x-y ) = t\\ $

$dx - dy = dt$
Now, given equation become
$dx+dy= \frac{dt}{t}$
Now, integrate both the sides
$x+ y + C '= \log t + C''$
Put $t = x- y$ again
$x+y = \log (x-y)+ C$
Now, by using boundary conditions we will find the value of C
It is given that
y = -1 when x = 0
$0+(-1) = \log (0-(-1))+ C\\$

$C = -1$
Now, put the value of C

$x+y = \log |x-y|-1\\ $

$\log|x-y|= x+y+1$
Therefore, the particular solution of the differential equation $(x - y) (dx + dy) = dx - dy,$ is $\log|x-y|= x+y+1$

Question 12 Solve the differential equation $\left[\frac{e^{-2\sqrt x}}{\sqrt x} - \frac{y}{\sqrt x} \right ]\frac{dx}{dy} = 1\; \ (x\neq 0)$ .

Answer:

Given,

$
\begin{aligned}
& {\left[\frac{e^{-2 \sqrt{x}}}{\sqrt{x}}-\frac{y}{\sqrt{x}}\right] \frac{d x}{d y}=1} \\
& \Rightarrow \frac{\mathrm{dy}}{\mathrm{dx}}=\frac{\mathrm{e}^{-2 \sqrt{x}}}{\sqrt{\mathrm{x}}}-\frac{\mathrm{y}}{\sqrt{x}} \\
& \Longrightarrow \frac{\mathrm{dy}}{\mathrm{dx}}+\frac{\mathrm{y}}{\sqrt{\mathrm{x}}}=\frac{\mathrm{e}^{-2 \sqrt{x}}}{\sqrt{\mathrm{x}}}
\end{aligned}
$


This is equation is in the form of $\frac{d y}{d x}+p y=Q$

$
p=\frac{1}{\sqrt{x}} \text { and } Q=\frac{e^{-2 \sqrt{x}}}{\sqrt{x}}
$


Now, I.F. $=\mathrm{e}^{\int \mathrm{pdx}}=\mathrm{e}^{\int \frac{1}{\sqrt{x}} \mathrm{dx}}=\mathrm{e}^{2 \sqrt{\mathrm{x}}}$
We know that the solution of the given differential equation is:

$
\begin{aligned}
& y(I \cdot F \cdot)=\int(Q \cdot F \cdot) d x+C \\
& \Rightarrow \mathrm{ye}^{2 \sqrt{\mathrm{x}}}=\int\left(\frac{\mathrm{e}^{-2 \sqrt{x}}}{\sqrt{\mathrm{x}}} \times \mathrm{e}^{2 \sqrt{\mathrm{x}}}\right) \mathrm{dx}+C \\
& \Rightarrow \mathrm{ye}^{2 \sqrt{\mathrm{x}}}=\int \frac{1}{\sqrt{\mathrm{x}}} \mathrm{dx}+\mathrm{C} \\
& \Rightarrow \mathrm{ye}^{2 \sqrt{x}}=2 \sqrt{\mathrm{x}}+C
\end{aligned}
$

Question 13: Find a particular solution of the differential equation $\frac{dy}{dx} + y \cot x = 4x \textup{cosec} x\ (x\neq 0)$ , given that $y = 0 \ \textup{when}\ x = \frac{\pi}{2}$ .

Answer:

Given equation is
$\frac{dy}{dx} + y \cot x = 4x \textup{cosec} x\ (x\neq 0)$
This is $\frac{dy}{dx} + py = Q$ type where $p =\cot x$ and $Q = 4xcosec x$ $Q = 4x \ cosec x$
Now,
$I.F. = e^{\int pdx}= e^{\int \cot xdx}= e^{\log |\sin x|}= \sin x$
Now, the solution of given differential equation is given by relation
$y(I.F.) =\int (Q\times I.F.)dx +C$
$y(\sin x ) =\int (\sin x\times 4x \ cosec x)dx +C$
$y(\sin x) =\int(\sin x\times \frac{4x}{\sin x}) +C\\$

$\\ y(\sin x) = \int 4x + C\\ $

$y\sin x= 2x^2+C$
Now, by using boundary conditions we will find the value of C
It is given that y = 0 when $x= \frac{\pi}{2}$
at $x= \frac{\pi}{2}$
$0.\sin \frac{\pi}{2 } = 2.\left ( \frac{\pi}{2} \right )^2+C\\$

$\\ C = - \frac{\pi^2}{2}$
Now, put the value of C
$y\sin x= 2x^2-\frac{\pi^2}{2}$
Therefore, the particular solution is $y\sin x= 2x^2-\frac{\pi^2}{2}, (sinx\neq0)$

Question 14: Find a particular solution of the differential equation $(x+1)\frac{dy}{dx} = 2e^{-y} -1$ , given that $y = 0$ when $x = 0$

Answer:

Given equation is
$(x+1)\frac{dy}{dx} = 2e^{-y} -1$
we can rewrite it as
$\frac{e^ydy}{2-e^y}= \frac{dx}{x+1}\\$
Integrate both the sides
$\int \frac{e^ydy}{2-e^y}= \log |x+1|\\$
$\int \frac{e^ydy}{2-e^y}$
Put
$2-e^y = t\\$

$-e^y dy = dt$
$\int \frac{-dt}{t}=- \log |t|$
put $t = 2- e^y$ again
$\int \frac{e^ydy}{2-e^y} =- \log |2-e^y|$
Put this in our equation
$\log |2-e^y| + C'= \log|1+x| + C''\\$

$\log (2-e^y)^{-1}= \log (1+x)+\log C\\$

$\frac{1}{2-e^y}= C(1+x)$

Now, by using boundary conditions we will find the value of C
It is given that y = 0 when x = 0
at x = 0
$\frac{1}{2-e^0}= C(1+0)\\ C = \frac{1}{2}$
Now, put the value of C
$\frac{1}{2-e^y} = \frac{1}{2}(1+x)\\ $'

$\\ \frac{2}{1+x}= 2-e^y\\$

$\frac{2}{1+x}-2= -e^y\\$

$-\frac{2x-1}{1+x} = -e^y\\$

$y = \log \frac{2x-1}{1+x}$
Therefore, the particular solution is $y = \log \frac{2x-1}{1+x}, x\neq-1$

Question 15: The population of a village increases continuously at the rate proportional to the number of its inhabitants present at any time. If the population of the village was 20, 000 in 1999 and 25000 in the year 2004, what will be the population of the village in 2009?

Answer:

Let n be the population of the village at any time t.

According to question,

$\frac{dn}{dt} = kn\ \ (k\ is\ a\ constant)$

$\\ \implies \int \frac{dn}{n} = \int kdt \\$

$\implies \log n = kt + C$

Now, at t=0, n = 20000 (Year 1999)

$\\ \implies \log (20000) = k(0) + C \\$

$\implies C = \log2 + 4$

Again, at t=5, n= 25000 (Year 2004)

$\\ \implies \log (25000) = k(5) + \log2 + 4 \\$

$\implies \log 25 + 3 = 5k + \log2 +4 \\$

$\implies 5k = \log 25 - \log2 -1 =\log \frac{25}{20} \\$

$\implies k = \frac{1}{5}\log \frac{5}{4}$

Using these values, at t =10 (Year 2009)

$\\ \implies \log n = k(10)+ C \\$

$\implies \log n = \frac{1}{5}\log \frac{5}{4}(10) + \log2 + 4 \\$

$\implies \log n = \log(\frac{25.2.10000}{16}) = \log(31250) \\$

$\therefore n = 31250$

Therefore, the population of the village in 2009 will be 31250.

Question 16: The general solution of the differential equation $\frac{ydx - xdy}{y} = 0$ is

(A) $xy = C$

(B) $x = Cy^2$

(C) $y = Cx$

(D) $y = Cx^2$

Answer:

Given equation is
$\frac{ydx - xdy}{y} = 0$
we can rewrite it as
$dx = \frac{x}{y}dy\\$

$\frac{dy}{y}=\frac{dx}{x}$
Integrate both the sides
we will get
$\log |y| = \log |x| + C\\ $

\log \frac{y}{x} = C \\ $

$\frac{y}{x} = e^C\\$

$\frac{y}{x} = C\\$

$y = Cx$
Therefore, answer is (C)

Question 17: The general solution of a differential equation of the type $\frac{dx}{dy} + P_1 x = Q_1$ is

(A) $ye^{\int P_1 dy} = \int \left(Q_1 e^{\int P_1 dy} \right )dy +C$

(B) $ye^{\int P_1 dx} = \int \left(Q_1 e^{\int P_1 dx} \right )dx +C$

(C) $xe^{\int P_1 dy} = \int \left(Q_1 e^{\int P_1 dy} \right )dy +C$

(D) $xe^{\int P_1 dx} = \int \left(Q_1 e^{\int P_1 dx} \right )dx +C$

Answer:

Given equation is
$\frac{dx}{dy} + P_1 x = Q_1$
and we know that the general equation of such type of differential equation is

$xe^{\int p_1dy} = \int (Q_1e^{\int p_1dy})dy+ C$
Therefore, the correct answer is (C)

Question 18: The general solution of the differential equation $e^x dy + (y e^x + 2x) dx = 0$ is

(A) $xe^y + x^2 = C$

(B) $xe^y + y^2 = C$

(C) $ye^x + x^2 = C$

(D) $ye^y + x^2 = C$

Answer:

Given equation is
$e^x dy + (y e^x + 2x) dx = 0$
we can rewrite it as
$\frac{dy}{dx}+y=-2xe^{-x}$
It is $\frac{dy}{dx}+py=Q$ type of equation where $p = 1 \ and \ Q = -2xe^{-x}$
Now,
$I.F. = e^{\int p dx }= e^{\int 1dx}= e^x$
Now, the general solution is
$y(I.F.) = \int (Q\times I.F.)dx+C$
$y(e^x) = \int (-2xe^{-x}\times e^x)dx+C\\$

$ye^x= \int -2xdx + C\\$

$ye^x=- x^2 + C\\ $

$ye^x+x^2 = C$
Therefore, (C) is the correct answer

Also check-

Topics covered in Chapter 9 Differential Equations: Miscellaneous Exercise


TopicsDescriptionExample
Variable Separable MethodUsed when the equation can be rearranged to separate variables x and y on opposite sides.$\begin{aligned} & \text { Solve: } \frac{d y}{d x}=x\left(1+y^2\right) \\ & \Rightarrow \frac{1}{1+y^2} d y=x d x \\ & \Rightarrow \tan ^{-1} y=\frac{x^2}{2}+C\end{aligned}$
Homogeneous Differential EquationsEquations where both numerator and denominator are homogeneous functions of the same degree. Substitution y=vx is used.Solve: $\frac{d y}{d x}=\frac{x+y}{x}$
Let $y=v x$, then reduce and solve.
Linear Differential EquationsFirst-order equations of the form \frac{d y}{d x}+P(x) y=Q(x). Solved using integrating factor (IF).Solve: $\frac{d y}{d x}+y=e^x$ IF $=e^{\int 1 d x}=e^x$, then multiply and integrate.
Exact Differential EquationsWhen a DE is of the form $M(x, y) d x+N(x, y) d y=0$ and satisfies $\frac{\partial M}{\partial y}=\frac{\partial N}{\partial x}$.Solve: $\left(2 x y+y^2\right) d x+\left(x^2+2 x y\right) d y=0$
Check for exactness and integrate accordingly.
Word Problems/ApplicationsReal-life problems involving growth, decay, cooling, etc., modeled and solved using DEs.A population grows at a rate proportional to its size. If it doubles in 3 years, find it after 5 years.
Solving Using Initial ConditionsAfter solving, use a given point (like y(x0)=y0) to find the constant of integration C.General: $y=C e^x$, given $y(0)=2 \Rightarrow 2=C \Rightarrow$ Particular $y=2 e^x$
Order and Degree of a Differential EquationIdentifying the order (highest derivative) and degree (power of highest derivative when equation is polynomial in derivatives).\text { For }\left(\frac{d^2 y}{d x^2}\right)^3+y=0 \text { : Order }=2 \text {, Degree }=3
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Frequently Asked Questions (FAQs)

Q: How many miscellaneous examples are given in the NCERT book?
A:

Four miscellaneous examples are given in the NCERT Class 12 Maths chapter, Differential Equations.

Q: What are the topics covered in the first exercise of the chapter?
A:

The first exercise covers the topic order and degree of differential equations

Q: What is the topic covered in the last exercise of the chapter?
A:

Solutions to linear differential equations

Q: Why do we solve Class 12 Maths chapter 9 miscellaneous solutions?
A:

After completing the chapter students can test their knowledge through miscellaneous exercises since it covers questions from all main topics of the chapter. 

Q: What is the number of exercises covered in the chapter Differential Equations?
A:

Seven including the miscellaneous exercise.

Q: Give the number of questions covered in the miscellaneous exercise?
A:

18 questions are covered in the miscellaneous exercise of chapter 9 Class 12 NCERT book

Q: What number of objective questions are covered in the NCERT solutions for Class 12 Maths chapter 9 miscellaneous exercise?
A:

3 multiple choice questions with 4 options for each are covered in the  Class 12 Maths chapter 9 miscellaneous exercise .

Q: What are the main topics covered in the chapter?
A:

The main topics covered in the chapter are order and degree, general and peculiar solutions of differential equations, formation of the differential equation for which general solution is given and a few methods to solve differential equations.

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From the academic year 2026, the board will conduct the CBSE 10th exam twice a year, while the CBSE 12th exam will be held once, as per usual. For class 10th, the second phase exam will act as the supplementary exam. Check out information on w hen the CBSE first exam 2026 will be conducted and changes in 2026 CBSE Board exam by clicking on the link .

If you want to change your stream to humanities after getting a compartment in one subject in the CBSE 12th Board Exam , you actually have limited options to qualify for your board exams. You can prepare effectively and appear in the compartment examination for mathematics again. If you do not wish to continue with the current stream, you can take readmission in the Humanities stream and start from Class 11th again, and continue studying for two more years to qualify for the 12th examination.

The GUJCET Merit List is prepared based on the Class 12th marks and GUJCET marks received by the students. CBSE students who are not from the Gujarat board can definitely compete with GSEB students, as their eligibility is decided based on the combined marks scored by them in GUJCET and the 12th board. The weightage of the GUJCET score is 40% and the weightage of the class 12 scores is 60%.