verycaodan
幼苗
共回答了20个问题采纳率:100% 举报
通项为(n+1-k)/[k*(k+1)*(k+2)]
=(n+1)/[k*(k+1)*(k+2)]-1/[(k+1)*(k+2)]
=(n+1)/[2k*(k+1)]-(n+1)/[2(k+1)*(k+2)]-1/(k+1)+1/(k+2)
所以n/1*2*3+(n-1)/2*3*4+…1/n*(n+1)(n+2)
=(n+1)/[2*1*(1+1)]-(n+1)/[2(n+1)*(n+2)]-1/(1+1)+1/(n+2)
=(n-1)/4+1/[2(n+2)]
1年前
2