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Establish or refute the propsed identity tan^2(a)-cos^2(a)= sin^2(a).

Hello, Quote: Originally Posted by christenc05 Establish or refute the propsed identity tan^2(a)-cos^2(a)= sin^2(a). $\displaystyle \Longleftrightarrow \tan^2(a)=\sin^2(a)+\cos^2(a)$ $\displaystyle \Longleftrightarrow \tan^2(a)=1$ One can see that this is not true for any value of a :)