（1+(1/n2)+(1/(n+1)2))=(n^4+2n^3+3n^2+2n+1)/n^2(n+1)^2=(n^2+n+1)^2/n^2(n+1)^2√（1+(1/n2)+(1/(n+1)2))=(n^2+n+1)/n(n+1)=1+1/n(n+1)
