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) ≤S≤lim (n→∞) n*n/(n^2+2)
1≤S≤1
因此极限是1
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) ≤S≤lim (n→∞) n*n/(n^2+2)
1≤S≤1
因此极限是1