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Homework Help: Trig Indentity Help

  1. Jan 23, 2010 #1
    1. The problem statement, all variables and given/known data
    Teacher gave this identity twice to us but the starting position slightly varies.

    Prove sec(2x) - tan(2x) = (cos(x)-sin(x))/(cos(x) + sin(x))

    Prove cos(2x)/(1 + sin(2x)) = tan(pi/4-x)


    2. Relevant equations
    pretty much all trig identities


    3. The attempt at a solution

    I get to (1-sin(2x))/cos(2x) = (cos(x)-sin(x))/(cos(x) + sin(x)) and then I'm stumped.
     
  2. jcsd
  3. Jan 23, 2010 #2

    tiny-tim

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    Welcome to PF!

    Hi Hockeystar! Welcome to PF! :wink:
    ok so far :rolleyes:

    now what is cos(2x) ? :smile:
     
  4. Jan 23, 2010 #3
    cosx - sinx(cosx + sinx). How does that help me cancel out something?
     
  5. Jan 23, 2010 #4

    tiny-tim

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    You mean (cosx - sinx)(cosx + sinx) …

    It doesn't have to cancel to help :wink:

    think! look at the RHS!
     
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