If for the solution curve y = f(x) of the differential equation dydx + ( x)y = 2 + x(1 + 2 x)2, x ( - 2, 2 ), f ( 3 ) = 310, then f ( 4 ) is equal to:
- 5 - 32 2
- 4 - 214
- 9 3 + 310(4 + 3)
- 3 + 110(4 + 3)
Answer
(2) 4 - 214
Solution
Linear D.E.: I.F. =e x dx= x
y x= (2+ x) x(1+2 x)2dx= 2 x+1( x+2)2dx (multiply by 2x)
ddx ( x x+2 )= 2 x+1( x+2)2 ⇒ y x= x x+2+C
x= 3: 310 2= 3/25/2+C ⇒ C=0
f ( 4 )= x x x+2= 1/21/ 2+2= 14+ 2= 4- 214
Answer: (2)