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Math Help - trig fix

  1. #1
    Member srirahulan's Avatar
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    Post trig fix

    \frac{1+tan^2[\frac{\pi}4-a]}{1-tan^2[\frac{\pi}4-a]}=cos 2A Prove this
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  2. #2
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    Re: trig fix

    Assuming a = A?

    Have you tried to expand the LHS out with the compound angle formula for tan?

    Recall \displaystyle \tan (a\pm b)= \frac{\tan a \pm \tan b}{1\mp \tan a \tan b}
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  3. #3
    Member srirahulan's Avatar
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    Re: trig fix

    I tried this way but finally i get 1/sin2a.
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  4. #4
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    Re: trig fix

    Quote Originally Posted by srirahulan View Post
    \frac{1+tan^2[\frac{\pi}4-a]}{1-tan^2[\frac{\pi}4-a]}=cos 2A Prove this
    As written that statement is false.
    To see that let a=\frac{\pi}{4}

    If you change \cos(2a) to \csc(2a) then it is true.
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  5. #5
    Member srirahulan's Avatar
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    Re: trig fix

    yes,I can understand.
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