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How can the following two identities be verified?

1. (cos^2y)/(1-siny)=1+siny

2. sin^2a-sin^4a=cos^2a-cos^4a


change cos^2a to 1-sin^2a=(1-sina)(1+sina)

Thank you. I figured out the first one with your help, but I'm still stuck on the second. Any tips?

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