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Thread: series problem

  1. #1
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    series problem

    if $\displaystyle f(x)= \sum_{k=0}^{\infty} (cos^2x)^k$, then $\displaystyle f(\frac{\pi}{4})$ is
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  2. #2
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    $\displaystyle \cos^2(\frac\pi4) = \frac12$.
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  3. #3
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    So this is simply the geometric sum $\displaystyle \sum_{k=0}^\infty \left(\frac{1}{2}\right)^2$
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