Given:

Show that:

Looks right to me. But here's another way, just in case:

Draw a right triangle. Label one of the acute angles y. Since

,

.

Label the opposite side x and the adjacent side 1. Find the hypotenuse (s) by using the Pythagorean theorem:

Cosine is adjacent over hypotenuse, so

.

Squaring both sides gives you

.

01