你写得真不规范,我看错了.等等先...好了.1/(n+1)^2 > 1/(n+1)(n+2) = 1/(n+1) - 1/(n+2)这样全部加起来,原式>n*(1/(n+1) - 1/(2n+1))=n^2/(2n^2+3n+1)1/(n+1)^2 < 1/n(n+1) = 1/n - 1/(n+1)原式∞,以上两个式子的极...