math
posted by lindsay .
Simplify
cos Theta/4 cos theta/4  sin theta/4 sin theta/4.

math 
Reiny
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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