NCERT Solutions
Class 12 - Mathematics Part-2 - Chapter 9: DIFFERENTIAL EQUATIONS
Exercise 9.4

Question. 1

In each of the Exercises 1 to 10, show that the given differential equation is homogeneous and solve it:

\((x^2+xy)\,dy=(x^2+y^2)\,dx\)

Answer:

\((x-y)^2=Cx\,e^{-\frac{y}{x}}\)

Question. 2

In each of the Exercises 1 to 10, show that the given differential equation is homogeneous and solve it:

\(y'=\frac{x+y}{x}\)

Answer:

\(y=x\log|x|+Cx\)

Question. 3

In each of the Exercises 1 to 10, show that the given differential equation is homogeneous and solve it:

\((x-y)\,dy-(x+y)\,dx=0\)

Answer:

\(\tan^{-1}\left(\frac{y}{x}\right)=-\frac{1}{2}\log(x^2+y^2)+C\)

Question. 4

In each of the Exercises 1 to 10, show that the given differential equation is homogeneous and solve it:

\((x^2-y^2)\,dx+2xy\,dy=0\)

Answer:

\(x^2+y^2=Cx\)

Question. 5

In each of the Exercises 1 to 10, show that the given differential equation is homogeneous and solve it:

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

Answer:

\(\frac{1}{2\sqrt{2}}\log\left|\frac{x+\sqrt{2}y}{x-\sqrt{2}y}\right|=\log|x|+C\)

Question. 6

In each of the Exercises 1 to 10, show that the given differential equation is homogeneous and solve it:

\(x\,dy-y\,dx=\sqrt{x^2+y^2}\,dx\)

Answer:

\(y+\sqrt{x^2+y^2}=Cx^2\)

Question. 7

In each of the Exercises 1 to 10, show that the given differential equation is homogeneous and solve it:

\(\{x\cos(\frac{y}{x})+y\sin(\frac{y}{x})\}\,y\,dx=\{y\sin(\frac{y}{x})-x\cos(\frac{y}{x})\}\,x\,dy\)

Answer:

\(xy\cos\left|\frac{y}{x}\right|=C\)

Question. 8

In each of the Exercises 1 to 10, show that the given differential equation is homogeneous and solve it:

\(x\frac{dy}{dx}-y+x\sin(\frac{y}{x})=0\)

Answer:

\(x\left[1-\cos\left(\frac{y}{x}\right)\right]=C\sin\left(\frac{y}{x}\right)\)

Question. 9

In each of the Exercises 1 to 10, show that the given differential equation is homogeneous and solve it:

\(y\,dx+x\log\left(\frac{y}{x}\right)\,dy-2x\,dy=0\)

Answer:

\(cy=\log\left|\frac{y}{x}\right|-1\)

Question. 10

In each of the Exercises 1 to 10, show that the given differential equation is homogeneous and solve it:

\((1+e^{\frac{x}{y}})\,dx+e^{\frac{x}{y}}\left(1-\frac{x}{y}\right)\,dy=0\)

Answer:

\(ye^{\frac{x}{y}}+x=C\)

Question. 11

For each of the differential equations in Exercises from 11 to 15, find the particular solution satisfying the given condition:

\((x+y)\,dy+(x-y)\,dx=0;\ y=1\ \text{when}\ x=1\)

Answer:

\(\log(x^2+y^2)+2\tan^{-1}\left(\frac{y}{x}\right)=\frac{\pi}{2}+\log 2\)

Question. 12

For each of the differential equations in Exercises from 11 to 15, find the particular solution satisfying the given condition:

\(x^2\,dy+(xy+y^2)\,dx=0;\ y=1\ \text{when}\ x=1\)

Answer:

\(y+2x=3x^2y\)

Question. 13

For each of the differential equations in Exercises from 11 to 15, find the particular solution satisfying the given condition:

\([x\sin^2(\frac{y}{x})-y]dx+x\,dy=0;\ y=\frac{\pi}{4}\ \text{when}\ x=1\)

Answer:

\(\cot\left(\frac{y}{x}\right)=\log|ex|\)

Question. 14

For each of the differential equations in Exercises from 11 to 15, find the particular solution satisfying the given condition:

\(\frac{dy}{dx}-\frac{y}{x}+\cosec(\frac{y}{x})=0;\ y=0\ \text{when}\ x=1\)

Answer:

\(\cos\left(\frac{y}{x}\right)=\log|ex|\)

Question. 15

For each of the differential equations in Exercises from 11 to 15, find the particular solution satisfying the given condition:

\(2xy+y^2-2x^2\frac{dy}{dx}=0;\ y=2\ \text{when}\ x=1\)

Answer:

\(y=\frac{2x}{1-\log|x|}\ \ (x\ne 0,\ x\ne e)\)

Question.  16

A homogeneous differential equation of the form \(\frac{dx}{dy}=h\left(\frac{x}{y}\right)\) can be solved by making the substitution.

(A)

\(y=vx\)

(B)

\(v=yx\)

(C)

\(x=vy\)

(D)

\(x=v\)

Question.  17

Which of the following is a homogeneous differential equation?

(A)

\((4x+6y+5)\,dy-(3y+2x+4)\,dx=0\)

(B)

\((xy)\,dx-(x^3+y^3)\,dy=0\)

(C)

\((x^3+2y^2)\,dx+2xy\,dy=0\)

(D)

\(y^2\,dx+(x^2-xy-y^2)\,dy=0\)

NCERT Solutions Class 12 – Mathematics Part-2 – Chapter 9: DIFFERENTIAL EQUATIONS – Exercise 9.4 | Detailed Answers