1/3*5+1/5*7+1/7*9……+1/19*21

问题描述:

1/3*5+1/5*7+1/7*9……+1/19*21
快。简便的要过程

1/3*5+1/5*7+1/7*9……+1/19*21
=2*(1/3-1/5+1/5-1/7+...+1/19-1/21)
=2*(1/3-1/21)
=4/7