=1 1/2-3+1/6+3 1/12-5+1/20+5 1/30-7+1/42+7 1/56-9+1/72+9 1/90（1-3+3-5+5-7+7-9+9）+(1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90)=1+(1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10)...