1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算_数学解答

1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算

人气：473 ℃　时间：2019-08-19 13:28:29

解答

=1/1* 1/2+1/2*1/3+1/3*1/4+...+1/9*1/10
=1/1-1/2+1/2-1/3+1/3-1/4+...+1/9-1/10
=1/1-1/10
=9/10