回復 3# maymay 的帖子
14 題,這是用黎曼和求極限
\(\displaystyle \sum\frac{1}{n}(1+\frac{k}{n})\sqrt{\frac{2k}{n}+(\frac{k}{n})^{2}}\to\int_{0}^{1} (1+x)\sqrt{2x+x^{2}}dx \)
然後變數代換 \( y=x^{2}+2x,\, dy=2(x+1)dx \)
\(\displaystyle \int_{0}^{1}(1+x)\sqrt{2x+x^{2}}dx=\frac{1}{3}y^{\frac{3}{2}}\Bigr|_{0}^{3}=\sqrt{3} \)