CBSE Class 12 Math 2009 Solved Paper

© examsnet.com
Question : 20
Total: 29
Find the particular solution, satisfying the given condition, for the following differential equation:
dy
dx
y
x
+ cosec (
y
x
)
= 0 , y = 0 when x = 1
Solution:  
dy
dx
y
x
+ cosec (
y
x
)
= 0 , y = 0 when x = 1
Let
y
x
= t ⇒ y = xt
dy
dx
= x
dt
dx
+ t
By substituting
dy
dx
in equation (i)
(x
dt
dx
+t
)
- t + cosex t = 0
⇒ x
dt
dx
= - cosec t
⇒ ∫
dt
cosect
+ ∫
dx
x
= 0
⇒ - cos t + log x = C ⇒ - cos (
y
x
)
+ log x = C
using y 0 when x 1
- 1 + 0 = C ⇒ C = - 1
So the solution is : cos (
y
x
)
= log x + 1
© examsnet.com
Go to Question: