# Math Help - tan identity

1. ## tan identity

I'm trying to develop a proof for:
tan(x+pi) - tan(pi-x) = 2tanx

I keep plugging it into the double angle formula, but I'm getting lost after trying to clear the denominator. Please help. Thanks!!

2. ## Re: tan identity

Double angle, or compound angle?

3. ## Re: tan identity

Originally Posted by ThanksForHelp
I'm trying to develop a proof for:
tan(x+pi) - tan(pi-x) = 2tanx
Do you know that $\tan(x+\pi)=\tan(x)=\tan(x-\pi)~?$

4. ## Re: tan identity

Originally Posted by Plato
Do you know that $\tan(x+\pi)=\tan(x)=\tan(x-\pi)~?$
Oh, periodic formula.....tan(x+pi n) = tanx - I don't understand the tan(x-pi), but that's OK. I can also use the fact that tan is an odd function to get it in the proper form. Thanks now I got it! Great!!! Thanks again.