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Math Help - tan identity

  1. #1
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    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!!
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  2. #2
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    Re: tan identity

    Double angle, or compound angle?
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  3. #3
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    Re: tan identity

    Quote Originally Posted by ThanksForHelp View Post
    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)~?
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  4. #4
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    Re: tan identity

    Quote Originally Posted by Plato View Post
    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.
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