If the domain of the function f(x) = -1 ( 5 - x3 + 2x ) + 1 e(10 - x) is (- , ] [ , ) - \ \, then 6( + + + ) is equal to
- 66
- 68
- 70
- 67
Answer
(3) 70
Solution
For -1: -1 5 - x3 + 2x 1, x - 32
(i) 5 - x3 + 2x 1
2 - 3x3 + 2x 0
3x - 22x + 3 0
x < - 32 or x 23
(ii) 5 - x3 + 2x -1
x + 82x + 3 0
x -8 or x > - 32
(i) and (ii): x (- , -8] [ 23, )
For 1 e(10 - x): 10 - x > 0 and 10 - x 1
x < 10, x 9
Domain = (- , -8] [ 23, 10 ) - \9\
= -8, = 23, = 10, = 9
6( + + + ) = 6 (11 + 23 ) = 66 + 4 = 70
Answer: (3)