CBSE Class 12 Math 2009 Solved Paper

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Question : 20 of 29
 
Marks: +1, -0
Find the particular solution, satisfying the given condition, for the following differential equation:
dydx−yx + cosec (yx) = 0 , y = 0 when x = 1
Solution:
dydx−yx + cosec (yx) = 0 , y = 0 when x = 1
Let yx = t ⇒ y = xt
⇒ dydx = x dtdx + t
By substituting dydx in equation (i)
(xdtdx+t) - t + cosex t = 0
⇒ x dtdx = - cosec t
⇒ ∫ dtcosect + ∫ dxx = 0
⇒ - cos t + log x = C ⇒ - cos (yx) + log x = C
using y 0 when x 1
- 1 + 0 = C ⇒ C = - 1
So the solution is : cos (yx) = log x + 1
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