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Math Help - identity question

  1. #1
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    identity question

    i am also having trouble with this identity!

    tan ( pi /4 + x ) - tan ( pi /4 - x ) = 2 sinx cosx
    tan ( pi /4 + x ) + tan ( pi /4 - x )

    EDITTED!
    Last edited by finalfantasy; November 4th 2007 at 12:41 PM.
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  2. #2
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    It is wrong because
    \tan (\pi + x) = \tan x and \tan (\pi - x) = - \tan x
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  3. #3
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    sorry about that, editted!
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  4. #4
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    The first step is to realize that,
    \tan (\pi/4 + x) = \frac{\tan \pi/4 + \tan x}{1 - \tan \pi/4 \cdot \tan x} = \frac{1+\tan x}{1-\tan x}
    Similarly,
    \tan (\pi/4 - x) = \frac{1-\tan x}{1+\tan x}.

    Now, simplify the fraction and see what you get.
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  5. #5
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    Cool

    That's what I did, but the answer is not coming up.

    Do I have to do something to the left side?
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