Let y = y(x) be the solution of the differential equation x dydx - 2y = x3 (2 - x3 ) 2 y, x 0. If y(2) = 0, then (y(1)) is equal to
- - 74
- - 34
- 34
- 74
Answer
(4) 74
Solution
Divide by 2 y:
x 2 y dydx - 2 y = x3(2 - x3)
Put y = t 2 y dydx = dtdx
dtdx - 2xt = x2(2 - x3) (linear)
I.F. = e- 2xdx = 1x2
ddx ( tx2 ) = 2 - x3
tx2 = 2x - x44 + C
y(2) = 0 t = 0 at x = 2: 0 = 4 - 4 + C C = 0
y = x2 (2x - x44 )
At x = 1: (y(1)) = 2 - 14 = 74
Answer: (4)