Aakash Repeater Courses
Take Aakash iACST and get instant scholarship on coaching programs.
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.
This Story also Contains
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
(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.
(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.
(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.
(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.
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 $y' = \frac{2y^2-x^2}{4xy}$
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}
$
Answer:
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 $\sin^{-1}y+\sin^{-1}x= C$
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.
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 $\cos y = \frac{\sec x}{\sqrt 2}$
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 \\ $
$\implies t = y + C$
$\Longrightarrow e^{\frac{x}{y}}=y+C$
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 $\log|x-y|= x+y+1$
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}
$
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 $y\sin x= 2x^2-\frac{\pi^2}{2}, (sinx\neq0)$
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 $y = \log \frac{2x-1}{1+x}, x\neq-1$
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 | Description | Example |
Variable Separable Method | Used 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 Equations | Equations 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 Equations | First-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 Equations | When 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/Applications | Real-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 Conditions | After 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 Equation | Identifying 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 |
Take Aakash iACST and get instant scholarship on coaching programs.
Also Read-
Frequently Asked Questions (FAQs)
The first exercise covers the topic order and degree of differential equations
Solutions to linear differential equations
After completing the chapter students can test their knowledge through miscellaneous exercises since it covers questions from all main topics of the chapter.
Seven including the miscellaneous exercise.
18 questions are covered in the miscellaneous exercise of chapter 9 Class 12 NCERT book
3 multiple choice questions with 4 options for each are covered in the Class 12 Maths chapter 9 miscellaneous exercise .
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.
On Question asked by student community
Hello
Yes, if you’re not satisfied with your marks even after the improvement exam, many education boards allow you to reappear as a private candidate next year to improve your scores. This means you can register independently, study at your own pace, and take the exams without attending regular classes. It’s a good option to improve your results and open up more opportunities for higher studies or careers. Just make sure to check the specific rules and deadlines of your education board so you don’t miss the registration window. Keep your focus, and you will do better next time.
Hello Aspirant,
Yes, in the case that you appeared for the 2025 improvement exam and your roll number is different from what was on the previous year’s marksheet, the board will usually release a new migration certificate. This is because the migration certificate will reflect the most recent exam details, roll number and passing year. You can apply to get it from your board using the process prescribed by them either online or through your school/college.
Yes, if you miss the 1st CBSE exam due to valid reasons, then you can appear for the 2nd CBSE compartment exam.
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%.
Take Aakash iACST and get instant scholarship on coaching programs.
This ebook serves as a valuable study guide for NEET 2025 exam.
This e-book offers NEET PYQ and serves as an indispensable NEET study material.
As per latest syllabus. Physics formulas, equations, & laws of class 11 & 12th chapters
As per latest syllabus. Chemistry formulas, equations, & laws of class 11 & 12th chapters
As per latest 2024 syllabus. Study 40% syllabus and score upto 100% marks in JEE