Answer to Question #72619 in Math for sfe

Question

Let 2
a = cos( ) π ，Which of the following is true？
(a) a = −1 (b) 1 1
2
− < ≤− a (c) 1 0
2
− < ≤ a (d) 1 0
2
< a ≤ (e) 1 1
2
< ≤