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posted by lindsay on Thursday, May 9, 2013 at 1:21pm.
Simplify cos Theta/4 cos theta/4 - sin theta/4 sin theta/4.
recall cos 2A = cos^2 A - sin^2 A you have that pattern cos(Ø/4)cos(Ø/4) - sin(Ø/4)sin(Ø/4) = cos^2 (Ø/4) - sin^2 (Ø/4) = cos (Ø/2)
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