Sunday, 14 August 2016

trigonometry - Proof of a trigonometric identity

I need to prove that:
1+cos(a+b)cos(ab)=cos2(a)+cos2(b)



I tried to start from both ways but it always took me back to the same one again
I tried also to prove that their - equal zero but I didn't work also

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real analysis - How to find limhrightarrow0fracsin(ha)h

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