Wednesday, December 10, 2025

25.11 - Solved Examples on Linear Differential Equations

In the previous section, we saw linear differential equations and the method to solve them. We saw some solved examples also. In this section, we will see a few more solved examples.

Solved example 25.62
Find the general solution of the differential equation $\boldsymbol{\frac{dy}{dx}~-~y~=~\cos x}$.
Solution
:
1. The given differential equation is:
$\small{\frac{dy}{dx}~-~y~=~\cos x}$
• Here P = −1 and Q = cos x

• P and Q must  satisfy any one of the following three conditions:
(i) Both P and Q are constants
(ii) Both P and Q are functions of x
(iii) P is a constant and Q is a function of x

• Here, P is a constant and Q is a function of x. So it is a first order linear differential equation.

2. Finding I.F = $\small{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}$  

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{\int{\left[{\rm{P}} \right]dx}}    & {~=~}    &{\int{\left[{\rm{-1}} \right]dx}~=~-x}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}    & {~=~}    &{e^{\left(-x \right)}}    \\
\end{array}}$

3. Write the equation with independent y:
$\small{y\left[{\rm{I.F}} \right]~=~\int{\left[{\rm{Q(I.F)}} \right]dx}}$

We get: $\small{y\left[e^{-x} \right]~=~\int{\left[\cos x~\times~e^{\left(-x \right)} \right]dx}}$

4. Do the integration in the R.H.S, and add the constant of integration.

We get: $\small{\frac{(\sin x~-~\cos x)e^{-x}}{2}~+~\rm{C}}$

• The reader must write all the steps involved in this integration.

5. Multiply the above result in (4), by the reciprocal of the I.F

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{y}    & {~=~}    &{\left[\frac{(\sin x~-~\cos x)e^{-x}}{2}~+~\rm{C} \right]\frac{1}{e^{-x}}}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{y}    & {~=~}    &{\frac{(\sin x~-~\cos x)}{2}~+~{\rm{C}}\,e^{x}}    \\
\end{array}}$

Solved example 25.63
Find the general solution of the differential equation $\boldsymbol{\frac{dy}{dx}~+~2y~=~\sin x}$.
Solution
:
1. The given differential equation is:
$\small{\frac{dy}{dx}~+~2y~=~\sin x}$
• Here P = 2 and Q = sin x

• P and Q must  satisfy any one of the following three conditions:
(i) Both P and Q are constants
(ii) Both P and Q are functions of x
(iii) P is a constant and Q is a function of x

• Here, P is a constant and Q is a function of x. So it is a first order linear differential equation.

2. Finding I.F = $\small{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}$  

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{\int{\left[{\rm{P}} \right]dx}}    & {~=~}    &{\int{\left[{\rm{2}} \right]dx}~=~2x}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}    & {~=~}    &{e^{\left(2x \right)}}    \\
\end{array}}$

3. Write the equation with independent y:
$\small{y\left[{\rm{I.F}} \right]~=~\int{\left[{\rm{Q(I.F)}} \right]dx}}$

We get: $\small{y\left[e^{2x} \right]~=~\int{\left[\sin x~\times~e^{\left(2x \right)} \right]dx}}$

4. Do the integration in the R.H.S, and add the constant of integration.

We get: $\small{\frac{(2\sin x~-~\cos x)e^{2x}}{5}~+~\rm{C}}$

• The reader must write all the steps involved in this integration.

5. Multiply the above result in (4), by the reciprocal of the I.F

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{y}    & {~=~}    &{\left[\frac{(2\sin x~-~\cos x)e^{2x}}{5}~+~\rm{C} \right]\frac{1}{e^{2x}}}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{y}    & {~=~}    &{\frac{2\sin x~-~\cos x}{5}~+~{\rm{C}}\,e^{-2x}}    \\
\end{array}}$

Solved example 25.64
Find the general solution of the differential equation $\boldsymbol{\cos^2 x \frac{dy}{dx}~+~y~=~\tan x~~\left(0\le x < \frac{\pi}{2} \right)}$.
Solution
:
1. The given differential equation is:
$\small{\cos^2 x \frac{dy}{dx}~+~y~=~\tan x~~\left(0\le x\le\frac{\pi}{2} \right)}$
Dividing both sides by $\small{\cos^2 x}$,we get:
$\small{\frac{dy}{dx}~+~\left(\sec^2 x \right) \,y~=~\left(\sec^2 x \right)\tan x~~\left(0\le x\le\frac{\pi}{2} \right)}$
• Here P = $\small{\sec^2 x}$ and Q = $\small{\left(\sec^2 x \right)\tan x}$

• P and Q must  satisfy any one of the following three conditions:
(i) Both P and Q are constants
(ii) Both P and Q are functions of x
(iii) P is a constant and Q is a function of x

• Here, both P and Q are functions of x. So it is a first order linear differential equation.

2. Finding I.F = $\small{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}$  

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{\int{\left[{\rm{P}} \right]dx}}    & {~=~}    &{\int{\left[\sec^2 x \right]dx}~=~\tan x}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}    & {~=~}    &{e^{\left(\tan x \right)}}    \\
\end{array}}$

3. Write the equation with independent y:
$\small{y\left[{\rm{I.F}} \right]~=~\int{\left[{\rm{Q(I.F)}} \right]dx}}$

We get: $\small{y\left[e^{\tan x} \right]~=~\int{\left[\left(\sec^2 x \right)\tan x~\times~e^{\left(\tan x \right)} \right]dx}}$

4. Do the integration in the R.H.S, and add the constant of integration.

We get: $\small{e^{\left(\tan x \right)}[\tan x~-~1]~+~\rm{C}}$

• The reader must write all the steps involved in this integration.

5. Multiply the above result in (4), by the reciprocal of the I.F

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{y}    & {~=~}    &{\left[e^{\left(\tan x \right)}[\tan x~-~1]~+~\rm{C} \right]\frac{1}{e^{\tan x}}}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{y}    & {~=~}    &{\tan x ~-~1~+~{\rm{C}}\,e^{-\tan x}}    \\
\end{array}}$

Solved example 25.65
Find the general solution of the differential equation $\boldsymbol{\frac{dy}{dx}~+~(\sec x)y~=~\tan x~~\left(0\le x < \frac{\pi}{2} \right)}$.
Solution
:
1. The given differential equation is:
$\small{\frac{dy}{dx}~+~(\sec x)y~=~\tan x~~\left(0\le x\le\frac{\pi}{2} \right)}$

• Here P = $\small{\sec x}$ and Q = $\small{\tan x}$

• P and Q must  satisfy any one of the following three conditions:
(i) Both P and Q are constants
(ii) Both P and Q are functions of x
(iii) P is a constant and Q is a function of x

• Here, both P and Q are functions of x. So it is a first order linear differential equation.

2. Finding I.F = $\small{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}$  

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{\int{\left[{\rm{P}} \right]dx}}    & {~=~}    &{\int{\left[\sec x \right]dx}~=~\log \left|\sec x~+~\tan x \right|}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}    & {~=~}    &{e^{\left(\log \left|\sec x~+~\tan x \right| \right)}~=~\left|\sec x~+~\tan x \right|}    \\
\end{array}}$

3. Write the equation with independent y:
$\small{y\left[{\rm{I.F}} \right]~=~\int{\left[{\rm{Q(I.F)}} \right]dx}}$

We get: $\small{y\left[\sec x~+~\tan x \right]~=~\int{\left[\tan x~\times~(\sec x~+~\tan x) \right]dx}}$

$\small{~=~\int{\left[\sec x\,\tan x~+~\tan^2 x) \right]dx}}$

• Given that $\small{\left(0\le x\le\frac{\pi}{2} \right)}$. This is the first quadrant. Cosine and tangent are +ve. So we can discard the absolute value symbol.

4. Do the integration in the R.H.S, and add the constant of integration.

We get: $\small{\sec x~+~\tan x~-~x~+~\rm{C}}$

• The reader must write all the steps involved in this integration.

5. Multiply the above result in (4), by the reciprocal of the I.F

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{y}    & {~=~}    &{\left[\sec x~+~\tan x~-~x~+~\rm{C} \right]\frac{1}{\sec x +\tan x}}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{y(\sec x +\tan x)}    & {~=~}    &{\sec x~+~\tan x~-~x~+~\rm{C}}    \\
\end{array}}$

Solved example 25.66
Find the general solution of the differential equation $\boldsymbol{x\,\frac{dy}{dx}~+~y~-~x~+~(xy)\cot x~=~0~~\left(x\ne0 \right)}$.
Solution
:
1. The given differential equation is:
$\small{x\,\frac{dy}{dx}~+~y~-~x~+~(xy)\cot x~=~0~~\left(x\ne0 \right)}$

Dividing by x and rearranging, we get:
$\small{\frac{dy}{dx}~+~\left(\frac{1}{x} \right)y~-~1~+~(y)\cot x~=~0}$

$\small{\Rightarrow\frac{dy}{dx}~+~\left(\frac{1}{x}~+~\cot x \right)y~-~1~=~0}$

$\small{\Rightarrow \frac{dy}{dx}~+~\left(\frac{1}{x}~+~\cot x \right)y~=~1}$

• Here P = $\small{\left(\frac{1}{x}~+~\cot x \right)}$ and Q = $\small{1}$

• P and Q must  satisfy any one of the following three conditions:
(i) Both P and Q are constants
(ii) Both P and Q are functions of x
(iii) P is a constant and Q is a function of x

• Here, both P and Q are functions of x. So it is a first order linear differential equation.

2. Finding I.F = $\small{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}$  

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{\int{\left[{\rm{P}} \right]dx}}    & {~=~}    &{\int{\left[\frac{1}{x}~+~\cot x \right]dx}~=~\log \left|x \right|+\log \left|\sin x \right|}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{\int{\left[{\rm{P}} \right]dx}}    & {~=~}    &{\log\left[\left|x \right|~\times~\left|\sin x \right| \right]~=~\log\left[ \left|x\,\sin x \right| \right]}    \\
{~\color{magenta} 3    }    &{{\Rightarrow}}    &{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}    & {~=~}    &{e^{\left(\log\left[ x\,\sin x  \right] \right)}~=~x\,\sin x }    \\
\end{array}}$

3. Write the equation with independent y:
$\small{y\left[{\rm{I.F}} \right]~=~\int{\left[{\rm{Q(I.F)}} \right]dx}}$

We get: $\small{y\left[x\,\sin x  \right]~=~\int{\left[1~\times~x\,\sin x \right]dx}}$

4. Do the integration in the R.H.S, and add the constant of integration.

We get: $\small{\sin\left(x\right) - x \cos\left(x\right)~+~\rm{C}}$

• The reader must write all the steps involved in this integration.

5. Multiply the above result in (4), by the reciprocal of the I.F

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{y}    & {~=~}    &{\left[\sin\left(x\right) - x \cos\left(x\right)~+~\rm{C} \right]\frac{1}{x\,\sin x}}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{y}    & {~=~}    &{\frac{1}{x}~-~\cot x~+~\frac{\rm{C}}{x\,\sin x}}    \\
\end{array}}$

Solved example 25.67
For the differential equation $\boldsymbol{\frac{dy}{dx}~+~2y\,\tan x~=~\sin x}$; y = 0 when x = $\small{\frac{\pi}{3}}$, find the particular solution satisfying the given conditions.
Solution
:
1. The given differential equation is:
$\small{\frac{dy}{dx}~+~2y\,\tan x~=~\sin x}$

• Here P = $\small{2\tan x}$ and Q = $\small{\sin x}$

• P and Q must  satisfy any one of the following three conditions:
(i) Both P and Q are constants
(ii) Both P and Q are functions of x
(iii) P is a constant and Q is a function of x

• Here, both P and Q are functions of x. So it is a first order linear differential equation.

2. Finding I.F = $\small{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}$  

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{\int{\left[{\rm{P}} \right]dx}}    & {~=~}    &{\int{\left[2\tan x \right]dx}~=~(-2)\log \left|\cos x \right|}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{\int{\left[{\rm{P}} \right]dx}}    & {~=~}    &{\log\left[\sec^2 x \right]}    \\
{~\color{magenta} 3    }    &{{\Rightarrow}}    &{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}    & {~=~}    &{e^{\left(\log\left[\sec^2 x \right] \right)}~=~\sec^2 x}    \\
\end{array}}$

3. Write the equation with independent y:
$\small{y\left[{\rm{I.F}} \right]~=~\int{\left[{\rm{Q(I.F)}} \right]dx}}$

We get: $\small{y\left[\sec^2 x  \right]~=~\int{\left[\sin x~\times~\sec^2 x \right]dx}}$

4. Do the integration in the R.H.S, and add the constant of integration.

We get: $\small{\sec x~+~\rm{C}}$

• The reader must write all the steps involved in this integration.

5. Multiply the above result in (4), by the reciprocal of the I.F

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{y}    & {~=~}    &{\left[\sec x~+~\rm{C} \right]\frac{1}{\sec^2 x}}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{y}    & {~=~}    &{\cos x~+~\rm{C}\,\cos^2x}    \\
\end{array}}$

6. Now we can find the particular solution.
• Given that: y = 0 when x = $\small{\frac{\pi}{3}}$
• Substituting in the general solution, we get:

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{y}    & {~=~}    &{\cos x~+~\rm{C}\,\cos^2x}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{0}    & {~=~}    &{\cos \left(\frac{\pi}{3} \right)~+~\rm{C}\,\cos^2\left(\frac{\pi}{3} \right)}    \\
{~\color{magenta} 3    }    &{{\Rightarrow}}    &{0}    & {~=~}    &{\frac{1}{2}~+~\rm{C}\,\left(\frac{1}{4} \right)}    \\
{~\color{magenta} 4    }    &{{\Rightarrow}}    &{0}    & {~=~}    &{2~+~\rm{C}}    \\
{~\color{magenta} 5    }    &{{\Rightarrow}}    &{\rm{C}}    & {~=~}    &{-2}    \\
\end{array}}$

• So the particular solution is:

$\small{y~=~\cos x~-~2\cos^2x}$

Solved example 25.68
For the differential equation $\boldsymbol{\frac{dy}{dx}~-~3y\,\cot x~=~\sin (2x)}$; y = 2 when x = $\small{\frac{\pi}{2}}$, find the particular solution satisfying the given conditions.
Solution
:
1. The given differential equation is:
$\small{\frac{dy}{dx}~-~3y\,\cot x~=~\sin (2x)}$

• Here P = $\small{-3\cot x}$ and Q = $\small{\sin (2x)}$

• P and Q must  satisfy any one of the following three conditions:
(i) Both P and Q are constants
(ii) Both P and Q are functions of x
(iii) P is a constant and Q is a function of x

• Here, both P and Q are functions of x. So it is a first order linear differential equation.

2. Finding I.F = $\small{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}$  

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{\int{\left[{\rm{P}} \right]dx}}    & {~=~}    &{\int{\left[-3\cot x \right]dx}~=~(-3)\log \left|\sin x \right|}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{\int{\left[{\rm{P}} \right]dx}}    & {~=~}    &{\log\left[\csc^3 x \right]}    \\
{~\color{magenta} 3    }    &{{\Rightarrow}}    &{e^{\left(\int{\left[{\rm{P}} \right]dx} \right)}}    & {~=~}    &{e^{\left(\log\left[\csc^3 x \right] \right)}~=~\csc^3 x}    \\
\end{array}}$

3. Write the equation with independent y:
$\small{y\left[{\rm{I.F}} \right]~=~\int{\left[{\rm{Q(I.F)}} \right]dx}}$

We get: $\small{y\left[\csc^3 x  \right]~=~\int{\left[\sin (2x)~\times~\csc^3 x \right]dx}}$

$\small{\Rightarrow y\left[\csc^3 x  \right]~=~\int{\left[\frac{2 \cos x}{\sin^2 x} \right]dx}}$

4. Do the integration in the R.H.S, and add the constant of integration.

We get: $\small{-2\csc x~+~\rm{C}}$

• The reader must write all the steps involved in this integration.

5. Multiply the above result in (4), by the reciprocal of the I.F

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{y}    & {~=~}    &{\left[-2\csc x~+~\rm{C} \right]\frac{1}{\csc^3 x}}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{y}    & {~=~}    &{-2\sin^2 x~+~\rm{C}\,\sin^3 x}    \\
\end{array}}$

6. Now we can find the particular solution.
• Given that: y = 2 when x = $\small{\frac{\pi}{2}}$
• Substituting in the general solution, we get:

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{y}    & {~=~}    &{-2\sin^2 x~+~\rm{C}\,\sin^3 x}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{2}    & {~=~}    &{-2 \sin^2 \left(\frac{\pi}{2} \right)~+~\rm{C}\,\sin^3\left(\frac{\pi}{2} \right)}    \\
{~\color{magenta} 3    }    &{{\Rightarrow}}    &{2}    & {~=~}    &{-2~+~\rm{C}}    \\
{~\color{magenta} 4    }    &{{\Rightarrow}}    &{\rm{C}}    & {~=~}    &{4}    \\
\end{array}}$

• So the particular solution is:

$\small{y~=~-2\sin^2 x~+~4\sin^3 x}$

Solved example 25.69
Find the general solution of the differential equation $\boldsymbol{(x+y)\frac{dy}{dx}~=~1}$.
Solution
:
1. The given differential equation is:

$\small{(x+y)\frac{dy}{dx}~=~1}$

• This can be rearranged as: $\small{\frac{dy}{dx}~=~\frac{1}{x+y}}$

• It is not a linear form. So we rearrange in another way: $\small{\frac{dx}{dy}~=~x+y}$

$\small{\Rightarrow \frac{dx}{dy}~-~x~=~y}$

• Here P1 = $\small{-1}$ and Q1 = $\small{y}$

• P1 and Q1 must  satisfy any one of the following three conditions:
(i) Both P1 and Q1 are constants
(ii) Both P1 and Q1 are functions of y
(iii) P1 is a constant and Q1 is a function of y

• Here, P1 is a constant and Q1 is a function of y. So it is a first order linear differential equation.

2. Finding I.F = $\small{e^{\left(\int{\left[{\rm{P}_1} \right]dy} \right)}}$

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{\int{\left[{\rm{P}_1} \right]dy}}    & {~=~}    &{\int{\left[-1 \right]dy}~=~-y}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{e^{\left(\int{\left[{\rm{P}_1} \right]dx} \right)}}    & {~=~}    &{e^{\left(-y \right)} }    \\
\end{array}}$

3. Write the equation with independent x:
$\small{x\left[{\rm{I.F}} \right]~=~\int{\left[{\rm{Q_1(I.F)}} \right]dy}}$

We get: $\small{x\left[e^{\left(-y \right)}  \right]~=~\int{\left[y~\times~e^{\left(-y \right)} \right]dy}}$

4. Do the integration in the R.H.S, and add the constant of integration.

We get: $\small{(-1)(y+1)e^{-y}~+~\rm{C}}$

• The reader must write all the steps involved in this integration.

5. Multiply the above result in (4), by the reciprocal of the I.F

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{x}    & {~=~}    &{\left[(-1)(y+1)e^{-y}~+~\rm{C} \right]\frac{1}{e^{-y}}}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{x}    & {~=~}    &{(-1)(y+1)~+~{\rm{C}}\,e^y}    \\
{~\color{magenta} 3    }    &{{\Rightarrow}}    &{x+y+1}    & {~=~}    &{{\rm{C}}\,e^y}    \\
\end{array}}$

Solved example 25.70
Find the general solution of the differential equation $\boldsymbol{y dx~-~\left(x + 2y^2 \right)dy~=~0}$.
Solution
:
1. The given differential equation is:
$\small{y dx~-~\left(x + 2y^2 \right)dy~=~0}$

This can be rearranged as: $\small{\frac{dy}{dx}~=~\frac{y}{x + 2y^2}}$

It is not a linear form. So we rearrange in another way: $\small{\frac{dx}{dy}~=~\frac{x + 2y^2}{y}}$

$\small{\Rightarrow \frac{dx}{dy}~=~\left(\frac{1}{y} \right)x~+~2y}$

$\small{\Rightarrow \frac{dx}{dy}~-~\left(\frac{1}{y} \right)x~=~2y}$

• Here P1 = $\small{\frac{-1}{y}}$ and Q1 = $\small{2y}$

• P1 and Q1 must  satisfy any one of the following three conditions:
(i) Both P1 and Q1 are constants
(ii) Both P1 and Q1 are functions of y
(iii) P1 is a constant and Q1 is a function of y

• Here, both P1 and Q1 are functions of y. So it is a first order linear differential equation.

2. Finding I.F = $\small{e^{\left(\int{\left[{\rm{P}_1} \right]dy} \right)}}$  

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{\int{\left[{\rm{P}_1} \right]dy}}    & {~=~}    &{\int{\left[\frac{-1}{y} \right]dy}~=~-\log \left|y \right|}    \\
{~\color{magenta} 2    }    &{{\Rightarrow}}    &{e^{\left(\int{\left[{\rm{P}_1} \right]dx} \right)}}    & {~=~}    &{e^{\left(-\log \left|y \right| \right)} ~=~\left|y \right|^{-1}~=~\frac{1}{\left|y \right|}}    \\
\end{array}}$

3. Write the equation with independent x:
$\small{x\left[{\rm{I.F}} \right]~=~\int{\left[{\rm{Q_1(I.F)}} \right]dy}}$

We get: $\small{x\left[\frac{1}{y}  \right]~=~\int{\left[2y~\times~\frac{1}{y} \right]dy}~=~\int{\left[2 \right]dy}}$

4. Do the integration in the R.H.S, and add the constant of integration.

We get: $\small{2y~+~\rm{C}}$

5. Multiply the above result in (4), by the reciprocal of the I.F

$\small{\begin{array}{ll}{~\color{magenta}    1    }  &{{}}    &{x}    & {~=~}    &{\left[2y~+~\rm{C} \right]y}    \\
{~\color{magenta} 3    }    &{{\Rightarrow}}    &{x}    & {~=~}    &{2y^2~+~{\rm{C}}y}    \\
\end{array}}$


In the next section, we will see a few more solved examples.

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