用夹逼定理S=lim (n→∞) n*[1/(n^2+2) +1/(n^2+4 )+...+1/(n^2+2n)]lim (n→∞) n*[1/(n^2+2n) +1/(n^2+2n )+...+1/(n^2+2n)]≤S≤lim (n→∞) n*[1/(n^2+2) +1/(n^2+2 )+...+1/(n^2+2)]lim (n→∞) n*n/(n^2+2n) ...