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September 18, 2014

September 18, 2014

Posted by **Carol** on Friday, April 22, 2011 at 1:20pm.

cos(x+y) + cos(x-y)=2cosxcosy

- calculus -
**MathMate**, Friday, April 22, 2011 at 3:08pmcos(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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