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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
    [Broken]



    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

    lurflurf

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    That looks wrong. It is close to the identity.

    $$2\sin^2(x-\pi/4)=1-\sin(2x)$$
     
  4. Jun 15, 2013 #3

    ehild

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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.


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

    ehild

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

    2000sin2(500πt)=1000(1-cos(1000πt)).

    ehild
     
  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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