Let f(x) = dxx2/3 + 2x1/2, be such that f(0) = -26 + 24 e(2). If f(1) = a + b e(3), where a, b Z, then a + b is equal to :
- -5
- -11
- -18
- -26
Answer
(2) -11
Solution
Put x = t6 dx = 6t5 dt, x2/3 = t4, x1/2 = t3
f = 6t5t4 + 2t3 dt = 6t2t + 2 dt = 6 (t - 2 + 4t + 2 )dt
= 3t2 - 12t + 24 e(t + 2) + C, where t = x1/6
f(0) = 24 e 2 + C = -26 + 24 e 2 C = -26
f(1): t = 1 f(1) = 3 - 12 + 24 e 3 - 26 = -35 + 24 e 3
a = -35, b = 24
a + b = -11
Answer: (2)