4/1*3-8/3*5+12/5*7-16/7*9.-40/19*21
问题描述：
4/1*3-8/3*5+12/5*7-16/7*9.-40/19*21
答
4/1*3-8/3*5+12/5*7-16/7*9.-40/19*21
=1+1/3-1/3-1/5+1/5+1/7-1/7-1/9+……-1/19-1/21
=1-1/21
=20/21