1/2+1/6+1/12+1/20+1/30+1/42into、equal、=)

1/2+1/6+1/12+1/20+1/30+1/42into、equal、=)

=(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7