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Math Help - differential trig problem

  1. #1
    Junior Member
    Joined
    Jan 2009
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    68

    differential trig problem

    Show that d/dx (1+cos 2x/1-cos 2x) = -2 cotx cosec^2 x

    I'm thinking that I need to use cos 2x = cos^2 x - sin^2 x, but when? Before or after differentiating? I tried both and just made a big mess. I realise this question is probably easier than it seems but I'm just not seeing it.

    Thank you.
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  2. #2
    Super Member
    Joined
    Jan 2009
    Posts
    715
    Try to use the identity
    cos2x = 2(cosx)^2 - 1 and cos2x = 1 - 2(sinx)^2

    so 1 + cos2x = 2(cosx)^2 , 1 - cos2x = 2(sinx)^2

    Hope this can help you
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