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Math Help - Trig Integral

  1. #1
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    Dec 2010
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    Trig Integral

    Having trouble with this problem
    \int COS^2{3x}

    So I used my power reducing formula to get here

    \int \frac{1+cos6X}{2}

    I pull a .5 out front
    \frac12 \int cos6x

    U Sub
    u=6x \ du=6dx

    Put a 1/6 out front
    \frac{1}{12} \int cosUdu \\ = \\ \frac{1}{12}sinx + c

    My book has a different answer, but I think I am right?
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  2. #2
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    \dfrac{1+cos(6x)}{2}=\dfrac{1}{2}(1+cos(6x)) \neq \dfrac{1}{2}(cos(6x))
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  3. #3
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    Dec 2010
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    Ahh yes, thanks for correcting my mistake!
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