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Help with Double Angle Identities

  1. Nov 27, 2012 #1
    Help with Double Angle Identities!!!

    cos θ = 24/25

    The angle lies in quadrant 1; 0<θ<90

    Find sin2θ



    I know you would use either the formula cos^2θ - sin^2θ or 2sinθcosθ
    And I know that the answer is 339/625, but I do not know how to get that answer?
     
  2. jcsd
  3. Nov 27, 2012 #2

    Simon Bridge

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    Re: Help with Double Angle Identities!!!

    Use trig formulae and Pythagoras.
    It helps if you sketch the angle in a rt-angled triangle.
     
  4. Nov 28, 2012 #3

    lurflurf

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    Re: Help with Double Angle Identities!!!

    hint: first find sin θ
     
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