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Math Help - cos(x)*cos(2x) = 0.707. Find x

  1. #1
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    cos(x)*cos(2x) = 0.707. Find x

    If cos(x) * cos (2x) = 0.707[i.e 1/sqrt(2)]. Find x. I know the answer is approximately 20.5deg. (Approximated from 20.47deg]. I don't know how to get to this answer. Please explain in a step by step detailed manner. Thanking You in advance.
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  2. #2
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    Here's a hint to get you started: cos(2x)=cos(x+x).
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