等差数列前n项和问题求和：1+1/1+2+1/1+2+3+…+1/1+2+3+…+n

等差数列前n项和问题求和：1+1/1+2+1/1+2+3+…+1/1+2+3+…+n
等差数列前n项和问题
求和：1+1/1+2+1/1+2+3+…+1/1+2+3+…+n

等差数列前n项和问题求和：1+1/1+2+1/1+2+3+…+1/1+2+3+…+n
1+1/1+2+1/1+2+3+…+1/1+2+3+…+n
=1+1/3+1/6+.+1/(1+n)n/2
=1+1/3+1/6+.2/(1+n)n
=2[1/2+1/6+1/12+.+1/n(n+1)]
=2[1/1*2+1/2*3+1/3*4+.+1/n(n+1)]
=2[1-1/2+1/2-1/3+1/3-1/4+...1/n-1/(n+1)]
=2[1-1/(n+1)]
=2*n/(n+1)
=2n/(n+1)