If the domain of the function f(x) = -1 ( 1x2 - 2x - 2 ) is (- , ] [ , ] [ , ), then + + + is equal to
- 4
- 2
- 5
- 3
Answer
(1) 4
Solution
For -1t to be defined, -1 t 1. Let g(x) = x2 - 2x - 2 = (x - 1)2 - 3; then -1 1g(x) 1 holds exactly when |g(x)| 1 (and g(x) 0).
Case 1: g(x) 1
(x - 1)2 4
x -1 or x 3
Case 2: g(x) -1
(x - 1)2 2
1 - 2 x 1 + 2
So the domain is (- , -1] [1 - 2, 1 + 2] [3, ), which gives = -1, = 1 - 2, = 1 + 2, = 3.
+ + + = -1 + 2 + 3 = 4
Answer: (1)