Let y=y(x) be the solution of the differential equation dydx= (1+x+x2 ) (1-y+y2 ), y(0)= 12. Then (2y(1)-1) is equal to :
- 3 ( 11 36 )
- 32 ( 11 312 )
- 3 ( 11 312 )
- 32 ( 11 36 )
Answer
(3) 3 ( 11 312 )
Solution
Separating the variables gives dyy2 - y + 1 = (1 + x + x2) dx, and since y2 - y + 1 = (y - 12 )2 + ( 32 )2, integration gives
2 3 -1 ( 2y - 1 3 ) = x + x22 + x33 + C
With y(0) = 12 the left side is -10 = 0, so C = 0. At x = 1:
2 3 -1 ( 2y(1) - 1 3 ) = 1 + 12 + 13 = 116
-1 ( 2y(1) - 1 3 ) = 11 312
∴ 2y(1) - 1 = 3 ( 11 312 )
Answer: (3)