Let y = y(x) be the solution of the differential equation x dydx - y = x2 x, x (0, ). If y ( 2 ) = 2, then 6y ( 6 ) - 8y ( 4 ) is equal to :
- -3
- 3
- -
Answer
(3) -
Solution
x dydx - y = x2 x x dy - y dxx2 = x dx
d ( yx ) = x dx
yx = e( x) + C
y ( 2 ) = 2 1 = e 1 + C C = 1
y = x (1 + e x )
6y ( 6 ) = 6 6 (1 + e 12 ) = - e 2
8y ( 4 ) = 8 4 (1 + e 1 2 ) = 2 - e 2
6y ( 6 ) - 8y ( 4 ) = - 2 = -
Answer: (3)