-1/2-1/6-1/12-1/20-1/30-1/42
=-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
=-8/7
4/3-7/12+9/20-11/30+13/42-15/56
=1+1/3-1/3-1/4+1/4+1/5-1/5-1/6+1/6+1/7-1/7-1/8
=1-1/8
7/8