lim(1/(n^2)+2/(n^2)+…+n/(n^2)) =lim((1+2+3+...+n)/(n^2)) =lim((1+n)*n/(2n^2)) =lim((n^2+n)/(2n^2))比较最高次项的系数,得lim(1/(n^2)+2/(n^2)+…+n/(n^2))=1/2