NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations Ex 9.4

Get Free NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations Ex 9.4 PDF in Hindi and English Medium. Sets Class 12 Maths NCERT Solutions are extremely helpful while doing your homework. Differential Equations Exercise 9.4 Class 12 Maths NCERT Solutions were prepared by Experienced LearnCBSE.in Teachers. Detailed answers of all the questions in Chapter 9 Class 12 Differential Equations Ex 9.4 provided in NCERT Textbook.

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NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations Ex 9.4

For each of the following D.E in Q. 1 to 10 find the general solution:

Ex 9.4 Class 12 Maths Question 1.
$\frac { dy }{ dx } =\frac { 1-cosx }{ 1+cosx }$
Solution:
$\frac { dy }{ dx } =\frac { 1-cosx }{ 1+cosx }$
$\frac { dy }{ dx } =\frac { 1-cosx }{ 1+cosx } =\frac { { 2sin }^{ 2 }\left( \frac { x }{ 2 } \right) }{ { 2cos }^{ 2 }\left( \frac { x }{ 2 } \right) } ={ tan }^{ 2 }\left( \frac { x }{ 2 } \right)$
integrating both sides, we get
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 1

Ex 9.4 Class 12 Maths Question 2.
$\frac { dy }{ dx } =\sqrt { 4-{ y }^{ 2 } } (-2<y<2)$
Solution:
$\frac { dy }{ dx } =\sqrt { 4-{ y }^{ 2 } } \Rightarrow \int { \frac { dy }{ \sqrt { { 4-y }^{ 2 } } } } =\int { dx }$
$\Rightarrow { sin }^{ -1 }\frac { y }{ 2 } =x+C$
$\Rightarrow y=2sin(x+C)$

Ex 9.4 Class 12 Maths Question 3.
$\frac { dy }{ dx } +y=1(y\neq 1)$
Solution:
$\frac { dy }{ dx } +y=1\Rightarrow \int { \frac { dy }{ y-1 } } =-\int { dx }$
$\Rightarrow log(y-1)=-x+c\Rightarrow y=1+{ e }^{ -x }.{ e }^{ c }$
$Hence\quad y=1+{ Ae }^{ -x }$
which is required solution

Ex 9.4 Class 12 Maths Question 4.
sec² x tany dx+sec² y tanx dy = 0
Solution:
we have
sec² x tany dx+sec² y tanx dy = 0
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 4

Ex 9.4 Class 12 Maths Question 5.
$\left( { e }^{ x }+{ e }^{ -x } \right) dy-\left( { e }^{ x }-{ e }^{ -x } \right) dx=0$
Solution:
we have
$\left( { e }^{ x }+{ e }^{ -x } \right) dy-\left( { e }^{ x }-{ e }^{ -x } \right) dx=0$
Integrating on both sides
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 5

Ex 9.4 Class 12 Maths Question 6.
$\frac { dy }{ dx } =\left( { 1+x }^{ 2 } \right) \left( { 1+y }^{ 2 } \right)$
Solution:
$\frac { dy }{ { 1+y }^{ 2 } } =\left( { 1+x }^{ 2 } \right) dx$
integrating on both side we get
${ tan }^{ -1 }y={ x+\frac { 1 }{ 3 } }x^{ 3 }+c$
which is required solution

Ex 9.4 Class 12 Maths Question 7.
y logy dx – x dy = 0
Solution:
$\because \quad y\quad logy\quad dx=x\quad dy\Rightarrow \frac { dy }{ y\quad logy } =\frac { dx }{ x }$
integrating we get
tiwari academy class 12 maths Chapter 9 Differential Equations 7

Ex 9.4 Class 12 Maths Question 8.
${ x }^{ 5 }\frac { dy }{ dx } =-{ y }^{ 5 }$
Solution:
${ x }^{ 5 }\frac { dy }{ dx } =-{ y }^{ 5 }\Rightarrow \int { { y }^{ -5 }dy } =-\int { { x }^{ -5 }dx }$
$\Rightarrow -\frac { 1 }{ { y }^{ 4 } } =\frac { 1 }{ { x }^{ 4 } } +4c\Rightarrow { x }^{ -4 }+{ y }^{ -4 }=k$

Ex 9.4 Class 12 Maths Question 9.
solve the following
$\frac { dy }{ dx } ={ sin }^{ -1 }x$
Solution:
$\frac { dy }{ dx } ={ sin }^{ -1 }x\Rightarrow \int { dy } =\int { { sin }^{ -1 }xdx }$
integrating both sides we get
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 9

Ex 9.4 Class 12 Maths Question 10.
${ e }^{ x }tany\quad dx+{ (1-e }^{ x }){ sec }^{ 2 }dy=0$
Solution:
${ e }^{ x }tany\quad dx+{ (1-e }^{ x }){ sec }^{ 2 }dy=0$
we can write in another form
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 10

Find a particular solution satisfying the given condition for the following differential equation in Q.11 to 14.

Ex 9.4 Class 12 Maths Question 11.
$\left( { x }^{ 3 }+{ x }^{ 2 }+x+1 \right) \frac { dy }{ dx } ={ 2x }^{ 2 }+x;y=1,when\quad x=0$
Solution:
here
$dy=\frac { { 2x }^{ 2 }+x }{ \left( { x }^{ 3 }+{ x }^{ 2 }+x+1 \right) } dx$
integrating we get
tiwari academy class 12 maths Chapter 9 Differential Equations 11

Ex 9.4 Class 12 Maths Question 12.
$x\left( { x }^{ 2 }-1 \right) \frac { dy }{ dx } =1,y=0\quad when\quad x=2$
Solution:
$x\left( { x }^{ 2 }-1 \right) \frac { dy }{ dx } =1,y=0\quad when\quad x=2$
$\Rightarrow \int { dy } =\int { \frac { dy }{ x(x+1)(x-1) } }$
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 12

Ex 9.4 Class 12 Maths Question 13.
$cos\left( \frac { dy }{ dx } \right) =a,(a\epsilon R),y=1\quad when\quad x=0$
Solution:
$cos\left( \frac { dy }{ dx } \right) =a\quad \therefore \frac { dy }{ dx } ={ cos }^{ -1 }a$
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 13

Ex 9.4 Class 12 Maths Question 14.
$\frac { dy }{ dx } =ytanx,y=1\quad when\quad x=0$
Solution:
$\frac { dy }{ dx } =ytanx\Rightarrow \int { \frac { dy }{ y } } =\int { tanx\quad dx }$
=> logy = logsecx + C
When x = 0, y = 1
=> log1 = log sec0 + C => 0 = log1 + C
=> C = 0
∴ logy = log sec x
=> y = sec x.

Ex 9.4 Class 12 Maths Question 15.
Find the equation of the curve passing through the point (0,0) and whose differential equation ${ y }^{ I }={ e }^{ x }sinx$
Solution:
${ y }^{ I }={ e }^{ x }sinx$
$\Rightarrow dy={ e }^{ x }sinx\quad dx$
tiwari academy class 12 maths Chapter 9 Differential Equations 15

Ex 9.4 Class 12 Maths Question 16.
For the differential equation $xy\frac { dy }{ dx } =(x+2)(y+2)$ find the solution curve passing through the point (1,-1)
Solution:
The differential equation is $xy\frac { dy }{ dx } =(x+2)(y+2)$
or xydy=(x + 2)(y+2)dx
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 16

Ex 9.4 Class 12 Maths Question 17.
Find the equation of a curve passing through the point (0, -2) given that at any point (pc, y) on the curve the product of the slope of its tangent and y-coordinate of the point is equal to the x-coordinate of the point
Solution:
According to the question $y\frac { dy }{ dx } =x$
$\Rightarrow \int { ydy } =\int { xdx } \Rightarrow \frac { { y }^{ 2 } }{ 2 } =\frac { { x }^{ 2 } }{ 2 } +c$
0, – 2) lies on it.c = 2
∴ Equation of the curve is : x² – y² + 4 = 0.

Ex 9.4 Class 12 Maths Question 18.
At any point (x, y) of a curve the slope of the tangent is twice the slope of the line segment joining the point of contact to the point (-4,-3) find the equation of the curve given that it passes through (- 2,1).
Solution:
Slope of the tangent to the curve = $\frac { dy }{ dx }$
slope of the line joining (x, y) and (- 4, – 3)
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 18
tiwari academy class 12 maths Chapter 9 Differential Equations 18.1

Ex 9.4 Class 12 Maths Question 19.
The volume of a spherical balloon being inflated changes at a constant rate. If initially its radius is 3 units and offer 3 seconds it is 6 units. Find the radius of balloon after t seconds.
Solution:
Let v be volume of the balloon.
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 19

Ex 9.4 Class 12 Maths Question 20.
In a bank principal increases at the rate of r% per year. Find the value of r if Rs 100 double itself in 10 years
Solution:
Let P be the principal at any time t.
According to the problem
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 20

Ex 9.4 Class 12 Maths Question 21.
In a bank principal increases at the rate of 5% per year. An amount of Rs 1000 is deposited with this bank, how much will it worth after 10 years
Solution:
Let p be the principal Rate of interest is 5%
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 21

Ex 9.4 Class 12 Maths Question 22.
In a culture the bacteria count is 1,00,000. The number is increased by 10% in 2 hours. In how many hours will the count reach 2,00,000 if the rate of growth of bacteria is proportional to the number present
Solution:
Let y denote the number of bacteria at any instant t • then according to the question
NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations 22

Ex 9.4 Class 12 Maths Question 23.
The general solution of a differential equation $\frac { dy }{ dx } ={ e }^{ x+y }$ is
(a) ${ e }^{ x }+{ e }^{ -y }=c$
(b) ${ e }^{ x }+{ e }^{ y }=c$
(c) ${ e }^{ -x }+{ e }^{ y }=c$
(d) ${ e }^{ -x }+{ e }^{ -y }=c$
Solution:
(a) $\frac { dy }{ dx } ={ e }^{ x }.{ e }^{ y }\Rightarrow \int { { e }^{ -y }dy } =\int { { e }^{ x }dx }$
$\Rightarrow { e }^{ -y }={ e }^{ x }+k\Rightarrow { e }^{ x }+{ e }^{ -y }=c$

NCERT Solutions for Class 12 Maths Chapter 9 Differential Equations Hindi Medium Ex 9.4

NCERT Solutions for Class 12 Maths Exercise 9.4 of Differential Equations

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12 Maths exercise 9.4 all questions
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Ex 9.4 in Hindi medium