For a homework assignment I'm supposed to prove that sin(x)^2+cos(x)^2=1, using(adsbygoogle = window.adsbygoogle || []).push({}); onlythe following identities (along with algebraic operations):

sin(-x)=-sin(x)

cos(-x)=cos(x)

cos(x+y)=cos(x)cos(y)-sin(x)sin(y)

sin(x+y)=sin(x)cos(y)+cos(x)sin(y)

I can't figure this out, because as far as I know the identity can only be derived from the Pythagorean Theorem.

Any help would be much appreciated.

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# Homework Help: Deriving a trigonometric identity

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