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Homework Help: How? Which Trig Identityis that?

  1. Jun 15, 2013 #1
    How?? Which Trig Identityis that?

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

    2. Relevant equations

    3. The attempt at a solution
    sin^2 = 1- cos^2 ??
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jun 15, 2013 #2


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    Homework Helper

    That looks wrong. It is close to the identity.

  4. Jun 15, 2013 #3


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    Yes. one of the relevant equation is sin2θ=1-cos2θ.
    The other one is cos(2θ)=cos2θ-sin2θ. From these, you get the identity

    sin2θ=.5(1-cos(2θ)). Use it.

  5. Jun 15, 2013 #4
    but there is no sin..
  6. Jun 15, 2013 #5


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    The equation you wrote in the first post is wrong. Correctly, it should be:


  7. Jun 15, 2013 #6
    Awaks.. IT is solution of the Electrical Engineer : priniciples and application Hambley book.

    And they made it wrong. I asked the question though i was wrong.
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