对于n个正数x1,x2,...xn。记Sn=((x1^2+x2^2+...+xn^2)/n)^(1/2),An=(x1+x2+...+xn)/n,Gn=(x1*x2*...*xn )^(1/n)Hn=n/(1/x1+1/x2+...+1/xn)则有n元均值定理，Sn>=An>=Gn>=Hn。取等条件均为x1=x2=...=xn
