Do you know that $\displaystyle \tan(x+\pi)=\tan(x)=\tan(x-\pi)~?$
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.