1/2*3+1/3*4+1/4*5+1/5*6.+1/19*20
问题描述:
1/2*3+1/3*4+1/4*5+1/5*6.+1/19*20
答
1/2*3+1/3*4+1/4*5+1/5*6.+1/19*20
=1/2-1/3+1/3-1/4+...+1/19-1/20
=1/2-1/20
=9/20