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\item[(1)]$\displaystyle\frac{d}{dx}\int_0^{x^2}(x-t)\cos tdt$を計算せよ．
\item[(2)]$\displaystyle\lim_{n\to\infty}\sum_{k=0}^{n-1}\frac{1}{\sqrt{4n^2-k^2}}$の値を求めよ．
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