# Establish or refute

• Jul 9th 2008, 06:25 AM
christenc05
Establish or refute
Establish or refute the propsed identity tan^2(a)-cos^2(a)= sin^2(a).
• Jul 9th 2008, 06:39 AM
Moo
Hello,

Quote:

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 :)