2/1+6/1+12/1+20/1+30/1+42/1+56/1用简便方法计算

1/2+1/6+1/12+1/20+1/30+1/42+1/56
=1/2+1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8
=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
=1-1/8
=7/8本回答被网友采纳

1/2+1/6+1/12+1/20+1/30+1/42+1/56
= 1/(1*2)+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)
= 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 - 1/8
= 7/8

6/1+12/1+20/1+30/1+42/1+56/1用简便方法计算