# Math Help - Establish or refute

1. ## Establish or refute

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

2. Hello,

Originally Posted by christenc05
Establish or refute the propsed identity tan^2(a)-cos^2(a)= sin^2(a).
$\Longleftrightarrow \tan^2(a)=\sin^2(a)+\cos^2(a)$

$\Longleftrightarrow \tan^2(a)=1$

One can see that this is not true for any value of a