>>11

∫_{0}^{1} x^2 dx
= lim_{n→∞} 農{k = 1}^{n} (k/n)^2・(1/n)
= lim_{n→∞} (1/(n^3)) 農{k = 1}^{n} k^2
= lim_{n→∞} (1/(n^3))・(1/6)n(n + 1)(2 n + 1)
= lim_{n→∞} (1/6)(1 + 1}/n)(2 + 1/n)
= (1/6)・1・2
= 1/3