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Help with a proof

  1. Nov 21, 2007 #1
    1. The problem statement, all variables and given/known data

    sin4x/(1-cos4x) * (1-cos2x)/cos2x = tan x

    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Nov 21, 2007 #2

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Well, gosh, there seems to be some things missing! Do you really think saying "I don't feel like making any attempt at all" is a good way to convince people to help you?
     
  4. Nov 21, 2007 #3
    I have tried sin4x=sin(2x+2x)=2sin2xcos2x

    (2sin2x/(1-cos4x))*1-cos2x

    (2sin2x-2sin2xcos2x)/(1-cos4x)

    2sin2x(1-cos2X)/1-cos4x

    cos2x=1-2sin^2x

    cos4x= cos^2 2x + sin^2 2x

    can I do sin2x=sin(x+x)=sinxcosx+cosxsinx=sinx(2cosx)

    I end up with 4sinxcosx=tanx?
     
  5. Nov 21, 2007 #4
     
  6. Nov 21, 2007 #5

    rock.freak667

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    Homework Helper

    Let me start you off on an easier path
    [tex]\frac{sin4x}{1-cos4x} * \frac{1-cos2x}{cos2x}[/tex]

    remember that [itex]sin4x=2sin2xcos2x[/itex], you replace sin4x by that identity...will anything there cancel out and make the expression simpler to prove?

    EDIT:2sin2x(1-cos2X)/1-cos4x

    you're nearly there actually...remember [itex]cos2A=1-2sin^2A[/itex] if A=2x then you'll have an identity for cos4x...use it and you'll get it out
     
  7. Nov 21, 2007 #6
    Okay

    I am left with 2sin2x(1-cos2x)/-2sin^2 2x
    wow! okay then cos 2x=1-2sin^2x
    2sin^2x/-sin2X
    2sin^2x/-2sinxcosx=sin/cos wha la Thanks so very much!!!
     
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