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Math Help - trig verify the identify

  1. #1
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    trig verify the identify

    verify the identify:


    since cos2u=cos^2-sin^2

    would the same be applied to cos3u..as in = cos^3-sin^3, or am i wrong
    Last edited by algebra2; April 17th 2008 at 07:12 PM. Reason: anaLytical reasons
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  2. #2
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    Quote Originally Posted by algebra2 View Post
    verify the identify:


    since cos2u=cos^2-sin^2

    would the same be applied to cos3u..as in = cos^3-sin^3, or am i wrong
    cos(A + B) = cos(A)~cos(B) - sin(A)~sin(B)

    Soooo....
    cos(3 \theta) = cos(2\theta + \theta)

    = cos(2\theta)~cos(\theta) - sin(2\theta)~sin(\theta)

    and you can take it from here.

    -Dan
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