原式=1+1/6+1+1/12+1+1/20+1+1/30+1+1/42
=(1+1+1+1+1)+1/6+1/12+1/20+1/30+1/42
=5+(1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)
=5+1/2-1/7(中间的都约掉)
=5又5/14