We haven't done a Trigonometry problem in a while, so here we go!
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Do you know any half angle formulas? Do you know what ? So what are and ? Once you have that the rest is easy.
That serves as a good hint.
No final takers? Here's my solution. Spoiler: I prefer a slightly different approach than that given by HallsofIvy:
So for we get
Adding these gives 3/2.
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