JEE Main20204 Sep 2020Morning ShiftMathematicsDifferential EquationsActual
Let y = y ( x ) be the solution of the differential equation, x y ' - y = x 2 ( x cos x + sin x ) , x > 0 . If y ( π ) = π , then y ' ' π 2 + y π 2 is equal to :
Options
- A2 + π 2
- B1 + π 2 + π 2 4
- C2 + π 2 + π 2 4
- D1 + π 2
Correct answer
A. 2 + π 2
Step-by-step solution
Given x d y d x − y = x 2 xcos + sinx ⇒ dy dx − 1 x y = x xcosx + sinx ∴ I.F = e - l nx = 1 x ∴ Solution is y . 1 x = ∫ 1 x . x x cos x + sin x d x y x = ∫ x cos x + sin x dx y x = x sin x + C ∵ y π = π   ⇒ C = 1 y = x 2 sin x + x d y d x = x 2 cos x + 2 x sin x + 1 d 2 y d x 2 = - x 2 sin x + 2 x cos x + 2 sin x + 2 x cos x = − x 2 sin x + 4 x cos x + 2 sin x ∴ y '' π 2 + y π 2 = − π 2 4 + 0 + 2 + π 2 4 +