Question

HELP PLEASE! I need to derive an identity from a different identity and I do not know how!

Derive:
`sin^2x+cos^x=1` from
`cos(x+y)=cosxcosy-sinxsiny` using cos(0)=1

Answer 1

cos(0) = cos(x-x)=cos(x)*(cos-x)-sin(x)*sin(-x)=cos^2(x)-(-sin^2(x)) = sin^2(x)+cos^2(x) = cos(0) = 1