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Math Help - Double Angle Formulae

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    Double Angle Formulae

    If tan(x)=2 and x is element of [0, pi/2] find the values of

    a)tan(2x)

    b) sin(2x)

    c) cos(2x)

    This is what i did.
    Since tan(x)=2, that would mean tan(2x)=4, so therefore tan(2x)=2tan(2)/1-tan(4)
    Last edited by mr fantastic; May 1st 2011 at 03:00 AM. Reason: Merged posts.
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  2. #2
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    No...

    tan(2x) = 2tan(x)/{1 - [tan(x)]^2}.

    You know that tan(x) = 2, so what is tan(2x)?
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    Quote Originally Posted by johnsy123 View Post
    This is what i did.
    Since tan(x)=2, that would mean tan(2x)=4, so therefore tan(2x)=2tan(2)/1-tan(4)
    Quote Originally Posted by Prove It View Post
    No...

    tan(2x) = 2tan(x)/{1 - [tan(x)]^2}.

    You know that tan(x) = 2, so what is tan(2x)?
    Further hint:

    johnsy123: Your notation is terrible. tan^2(x) is not the same as tan(2x), so if tan(x) = 2 then tan^2(x) = 4. However your intention is correct in how you are trying to put it into the tan(2x) formula. Instead of tan(4), which is also not equal to tan^2(x), you want to use 4. Make sure you understand this.

    -Dan
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