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Thread: Prove the identity

  1. #1
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    Prove the identity

    cos 4 theta - sin 4 theta = cos2 theta
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  2. #2
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    Re: Prove the identity

    Is the right hand side cos (2 theta) or cos^2(theta)? Since you used exponents on the left I presume it is the former. In that case, use the fact that cos(2 theta)= 1- 2sin^2(theta) and that cos^2(theta)= 1- sin^2(theta).
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  3. #3
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    Re: Prove the identity

    Quote Originally Posted by Bonganitedd View Post
    cos 4 theta - sin 4 theta = cos2 theta
    I'd treat the LHS as the difference of 2 squares.
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