Question

The photo is attached

Answer 1

D

using the double - angle identity

cos (2A) = cos² A - sin² A = 2cos² A - 1 = 1 - 2sin² A

the right side = 1 - 2sin² (112.5° ) with A = 22.5°

hence 2A = 2 × 22.5° = 45°

thus cos 45° = 1 - 2sin² ( 22.5°)