原式为:1-5/6 +7/12 -9/20+11/30 -13/42
=1-(1/2 +1/3) +(1/3 +1/4)-(1/4+1/5)+(1/5 +1/6)-
(1/6+1/7)
=1-1/2 -1/3 +1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7
观察上式,中间的都抵消了,只剩下
1-1/2 -1/7
=1/2 -1/7
=5/14
原式为:1-5/6 +7/12 -9/20+11/30 -13/42
=1-(1/2 +1/3) +(1/3 +1/4)-(1/4+1/5)+(1/5 +1/6)-
(1/6+1/7)
=1-1/2 -1/3 +1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7
观察上式,中间的都抵消了,只剩下
1-1/2 -1/7
=1/2 -1/7
=5/14