1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110 用简便 急

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110 用简便 急
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110 用简便 急

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110 用简便 急
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110
=1/1*2+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7+1/7*8+1/8*9+1/9*10+1/10*11
=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+1/10-1/11
=1-1/11
=10/11

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90+1/110
=1/（1*2）+1/（2*3）+1/（3*4）+1/（4*5）_1/（5*6）+1/（6*7）+1/（7*8）+1/（8*9）+1/（9*10）+1/（10*11）
=1-1/2+1/2-1/3+1/3-1/4...+1/9-1/10+1/10-1/11
=1-1/11
=10/11中间的都笑掉了