If ( 1 - 5 2 x 5 x 2 x )dx = f(x) + C, where C is the constant of integration, then f ( 6 ) - f ( 4 ) is equal to
- 1 3(26 - 3)
- 4 3(8 - 6)
- 1 3(26 + 3)
- 2 3(4 + 6)
Answer
(2) 4 3(8 - 6)
Solution
Numerator: 1 - 5 2 x = 2 x - 4 2 x
1 - 5 2 x 5 x 2 x = 1 3 x 2 x - 4 5 x
Now ddx ( 1 4 x x ) = ddx ( -4x -1x )
= -4 -5x x -1x + -4x -2x x
= - 4 5 x + 1 3 x 2 x
f(x) = 1 4 x x (+ constant, which cancels in the difference)
f ( 6 ) = 1 116 32 = 32 3
f ( 4 ) = 1 14 1 2 = 4 2 = 4 6 3
f ( 6 ) - f ( 4 ) = 32 - 4 6 3
= 4 3(8 - 6)
Answer: (2)