You can put this solution on YOUR website! First we should rewrite cos 84 as sin 6 (these two are equal). Denote our desired answer A (which should turn out to be 1/16)
(remember sin 6 is the cos 84)
Suppose we multiply both sides by 16 cos 6:
Applying the double angle identity for sine, we have 2 sin 6 cos 6 = sin 12, and we replace sin 6 cos 6 with (1/2) sin 12 (here I will divide coefficient by 2)
We apply it again and again:
Here, sin 96 is equal to cos 6 (you can verify this either using the sum identity or the unit circle), so we can cancel them out, leaving
