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Math Help - Develop a formula for cosine

  1. #1
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    Develop a formula for cosine

    How to you develop a formula for sin(11`theta) as a degree- 11 polynomial in cos(`theta).
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  2. #2
    MHF Contributor kalagota's Avatar
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    Quote Originally Posted by christenc05 View Post
    How to you develop a formula for sin(11`theta) as a degree- 11 polynomial in cos(`theta).
    \sin (11\theta) = \sin (10\theta + \theta) = \sin(10\theta)\cos(\theta) + \sin(\theta)\cos(10\theta)

    = 2\sin(5\theta)\cos(5\theta)\cos(\theta) + \sin(\theta)[2\cos^2(5\theta) - 1]

    just continue the process of using the identities until the angle is \theta only and in terms of \cos \theta
    Last edited by kalagota; July 8th 2008 at 06:36 AM. Reason: forgot something..
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