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Math Help - Brainfog on Identity

  1. #1
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    Brainfog on Identity

    Hi
    I have to make the bottom one from the top two and have simply forgot how to get there



    2sinAcosA/cos^2A-Sin^2A

    or alternatives of cos2A..but I am losing my way!
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  2. #2
    MHF Contributor red_dog's Avatar
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    \tan 2A=\frac{\sin 2A}{\cos 2A}=\frac{2\sin A\cos A}{\cos^2A-\sin^2A}=

    =\frac{\dfrac{2\sin A\cos A}{\cos^2A}}{\dfrac{\cos^2A-\sin^2A}{\cos^2A}}=\frac{2\tan A}{1-\tan^2A}
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  3. #3
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    Smile

    I knew I would kick myself
    Many Thanks
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