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posted by Carol on Friday, April 22, 2011 at 1:20pm.
verify the following identity cos(x+y) + cos(x-y)=2cosxcosy
cos(a+b)=cos(a)cos(b)-sin(a)sin(b) cos(a-b)=cos(a)cos(b)+sin(a)sin(b) What happens when you add the two together?
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