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Homework Help: Proving this trignometric identity

  1. Jan 3, 2013 #1
    1. The problem statement, all variables and given/known data

    Prove that :

    [itex]\frac{cos(x)-1}{(1-cos(x))^{3}}[/itex] = -[itex]\frac{1}{4sin^{4}(0.5x)}[/itex]


    2. Relevant equations

    None that I can think of.
    Maybe the double angle formula...

    3. The attempt at a solution

    I couldn't do much in this question :

    -[itex]\frac{1}{(1-cos(x))^{2}}[/itex]
     
  2. jcsd
  3. Jan 3, 2013 #2
    Things to try: expand [itex](1-\cos(x))^2[/itex] and expressing [itex]\sin(x/2)[/itex] in terms of just sin and cos.
     
  4. Jan 3, 2013 #3

    ehild

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    Homework Helper

    Yes, use the double angle formula.

    ehild
     
  5. Jan 5, 2013 #4
    What exactly do you mean by that ?

    Should I expand it in powers of Sin(x)/Cos(x) ?
     
  6. Jan 5, 2013 #5
    Use double angle formula. What is cos(2x) in terms of sin? Similarly, what is cos(x)?
     
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