1/2+2/3+3/4+4/5+5/6+6/7
=(1-1/2)+(1-1/3)+(1-1/4)+(1-1/5)+(1-1/6)+(1-1/7)
=6-1/2-1/3-1/4-1/5-1/6-1/7
=6-(1/2+1/3+1/6)-(1/4+1/5+1/7)
=6-1-83/140
=5-83/140
=617/140
3/2+4/3+5/4+6/5+7/6
=1+1/2+1+1/3+1+1/4+1+1/5+1+1/6
=5+(1/2+1/3+1/6)+(1/4+1/5)
=5+1+9/20
=129/20
带进去算就是了
有点笨 好像