1/20+1/30+1/42+.+1/132+1/156=
问题描述：
1/20+1/30+1/42+.+1/132+1/156=
1-1/2-1/4-1/8-1/16-1/32-.1/1024=
还有一道:2+3 1/6+5 1/12+7 1/20+11 1/30+13 1/42=
还有:2/1×3×5+2/3×5×7+2/5×7×9+2/7×9×11=
2/11×13+2/13×15+2/15×17+2/17×19+2/19×21=
答
1/20+1/30+1/42+.+1/132+1/156=1/4-1/5+1/5-1/6+1/6-1/7+...-1/12+1/12-1/13=1/4-1/13=9/52（裂项相消）1-1/2-1/4-1/8-1/16-1/32-.1/1024=1-（1/2+1/4+1/8+1/16+...+1/1024）=1-1/2[1-（1/2）^10]/(1-1/2)=1-(1-1/10...