1+1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72=？（要用简便方法算）

来源：百度知道编辑：UC知道时间：2024/06/19 10:11:47

1+1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72
=1+1/1x2+1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8+1/8x9
=1+1/1+1/9(所有分母中相同数字都删去)
=2又1/9

不知道对不对,记得以前学过,但是放假这么久了又没作业都要忘光啦~~

1+1/2+1/6+1/12+1/20+1/30+1/42+1/56
=1+(1-1/2+1/2-1/3+1/3-1/4+....+1/6-1/7+1/7-1/8)
=1+(1-1/8)
=15/8

(1/2) (1/4+1/6)= 1/2+1/6+1/12+1/20+1/30 1/2+1/4+1/6+1/8+.......+1/n=? -1/2-1/6-1/12-1/20-``````````````-1/4026042 1/2+1/6+1/12+......+1/1980+1/2070=? (1/2-1)*(1/3-1)*(1/4-1)*(1/5-1)*(1/6-1)*(1/7-1)*(1/8-1)*(1/9-1)*(1/10-1) 1/2 ，1/3 ,1/6 /1/6 ,() (1-1/2)*(1-1/4)*(1-1/6)*...........*(1-1/10)解法 1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90= 1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?