用拆项法
1/2+1/6+1/20+1/30+1/42+1/56+1/72
=1/(1*2)+1/(2*3)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)
=1-1/2+1/2-1/3+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9
=1-1/3+1/4-1/9
=7/12
不过照常规来说,应该有1/12这一项的,是不是少打了,反正方法是一样的,拆项相消.
1/2+1/6+1/20+1/30+1/42+1/56+1/72=怎么算简便?
1个回答
相关问题
-
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=1怎么算简便?
-
简便计算：[1/20]+[1/30]+[1/42]+[1/56]+[1/72]．
-
2/1+6/1+12/1+20/1+30/1+42/1+56/1+72/1+90/1,简便运算,
-
1/20+1/30+1/42+1/56+1/72等于多少 简便
-
1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90简便计算
-
简算：1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
-
简算6/1+12/1+20/1+30/1+42/1+56/1+72/1+90/1
-
简便计算：1/30+1/42+1/56+1/72=
-
1／2 + 1／6 + 1／12 + 1／20 + 1／30+ 1／42 + 1／56 + 1／72＝
-
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72=?