1+1/2+1/6+1/12+1/20+1/30+1/42+1/56
=1+[1/2+1/（2x3）+1/12+1/20+1/30+1/42+1/56]
=1+（2/3+1/12+1/20+1/30+1/42+1/56）
=1+[2/3+1/(3*4)+1/20+1/30+1/42+1/56]
=1+（3/4+1/20+1/30+1/42+1/56）
=1+[3/4+1/(4x5)+1/30+1/42+1/56]
=1+（4/5+1/30+1/42+1/56）
=1+[4/5+1/(5x6)+1/42+1/56]
=1+（5/6+1/42+1/56）
=1+[5/6+1/(6x7)+1/56]
=1+（6/7+1/56）
=1+[6/7+1/(7x8)]
=1+7/8
=15/8 即1又7/8