If 01 4 -1 (1 - 2x + 4x2 )dx = a -1(2) - b e(5), where a, b N, then (2a + b) is equal to .
Answer
9
Solution
1 - 2x + 4x2 > 0, -1(1 - 2x + 4x2) = -1 11 + 2x(2x - 1)
= -1 2x - (2x - 1)1 + 2x(2x - 1) = -1(2x) - -1(2x - 1)
01 -1(2x - 1) dx = 0 (put u = 2x - 1: odd function on [-1, 1])
01 -1(2x) dx = 12 02 -1u du
= 12 [u -1u - 12 e(1 + u2) ]02 (by parts)
= -1(2) - 14 e 5
01 4 -1(1 - 2x + 4x2) dx = 4 -1(2) - e(5)
a = 4, b = 1
2a + b = 9
Answer: 9