Let the domain of the function f(x) = 2 4 6 (3 + 4x - x2) be (a, b). If 0b-a [x2] dx = p - q - r, p, q, r N, (p, q, r) = 1, where [ ] is the greatest integer function, then p + q + r is equal to
- 10
- 11
- 9
- 8
Answer
(1) 10
Solution
Domain: 4 6 (3 + 4x - x2) > 0
⇒ 6 (3 + 4x - x2) > 1
⇒ 3 + 4x - x2 > 6 ⇒ x2 - 4x + 3 < 0 ⇒ 1 < x < 3
⇒ a = 1, b = 3, b - a = 2
02 [x2] dx = 01 0 dx + 1 2 1 dx + 2 3 2 dx + 32 3 dx
= ( 2 - 1) + 2( 3 - 2) + 3(2 - 3)
= 5 - 2 - 3
⇒ p = 5, q = 2, r = 3
∴ p + q + r = 10
Answer: (1)