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The following pattern: $\frac{3^{2/401}}{3^{2/401} +3}+\frac{3^{4/401 }}{3^{4/401} +3}+\frac{3^{6/401}}{3^{6/401} +3}+\frac{3^{8/401}}{3^{8/401} +3}$

what will the result be if the pattern is continued $\;300\;$ times?

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    Your teacher seems to be a humorous man... :-)2012-12-09

2 Answers 2

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If you need the sum to the nth term, you're looking at computing the sum of the first 300 terms:

$\sum_{k=1}^{300}\left(\large\frac{3^{\frac{2k}{401}}}{3^{\frac{2k}{401}}+3}\right)$

To sum to the nth term, you need to compute:

$\sum_{k=1}^{n}\left(\large\frac{3^{\frac{2k}{401}}}{3^{\frac{2k}{401}}+3}\right)= \sum_{k=1}^{n}\left(\large\frac{3\cdot 3^{\frac{2k-1}{401}}}{3\cdot\left(3^{\frac{2k-1}{401}}+1\right)}\right) = \sum_{k=1}^{n}\left(\large\frac{3^{\frac{2k-1}{401}}}{\left(3^{\frac{2k-1}{401}}+1\right)}\right)$

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I highly doubt there is a simple closed form for this. WolframAlpha only returns (query) the decimal approximation: $130.6386445...$

Also, the inverse symbolic lookup calculator doesn't find anything...