1比2乘3+1比3乘4+1比4乘5+...+1比19乘20_数学解答

1比2乘3+1比3乘4+1比4乘5+...+1比19乘20

人气：253 ℃　时间：2019-10-19 00:47:04

解答

1/(2×3)+1/(3×4)+1/(4×5)+……+1/(19×20)
=1/2-1/3+1/3-1/4+1/4-1/5+……+1/19-1/20
=1/2-1/20
=10/20-1/20
=9/20