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Need help with proofs, please!

  1. Nov 12, 2007 #1
    1. The problem statement, all variables and given/known data

    prove:
    sin3x = sinx (3-4sin^2x)

    tanx+sinx/2tanx = cos^2(x/2)

    cot2x = (cot^2 x-1)/(2cotx)

    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
    Last edited: Nov 12, 2007
  2. jcsd
  3. Nov 12, 2007 #2

    rock.freak667

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    Homework Helper

    ....where is your attempt?
    But anyhow...for the first one...rewrite sin3x as sin(2x+x)

    and well for the second and third ones..try simplifying it into sin and cos only , for the last one...remember that cot(x)=1/tan(x)
     
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