Question

Rewrite 1−2 sin ^2 (22.5∘) using a double-angle identity.

Answer 1

Using the identity :

Cos (2a) = 1-2 Sin^2(a)

Therefore :1−2 sin ^2 (22.5∘) = Cos(2a)
                                                = Cos (2 * 22.5) = Cos 45