1+1/﹙2+1﹚+1/﹙3+2+1)+……+1/﹙1+2+3+4+5+.+n﹚
=1+2/(2x3)+2/(3x4)+……+2/n(n+1)
=1+2x[1/2-1/3+1/3-1/4+……+1/n-1/(n+1)]
=1+2x[1/2-1/(n+1)]
=1+1-2/(n+1)
=2n/(n+1)
1+1/﹙2+1﹚+1/﹙3+2+1)+……+1/﹙1+2+3+4+5+.+n﹚
=1+2/(2x3)+2/(3x4)+……+2/n(n+1)
=1+2x[1/2-1/3+1/3-1/4+……+1/n-1/(n+1)]
=1+2x[1/2-1/(n+1)]
=1+1-2/(n+1)
=2n/(n+1)