Answer:
See below.
Explanation:
Using the identity sin^2x - sin^2x = cos 2x
cos^2( π/4 - Ф/4) - sin^2(π/4 - Ф/4) = cos 2(π/4 - Ф/4)
= cos(π/2 - Ф/2)
Now cos(π/2 - Ф/2) = cosπ/2 cos Ф/2 + sin π/2 sin Ф/2
But cos π/2 = 0 and sin π/2 = 1 so
cos(π/2 - Ф/2) = 0 * cos Ф/2 + 1 * sin Ф/2
= sin Ф/2.
