1/2+1/6+1/12+1/20+.+1/90=?

分类: 作业答案 • 2021-12-19 12:04:43

问题描述：

答

1-1/2+1/2-1/3+1/3-1/4+1/4.......+1/89-1/89+1/90
=1+1/90
=91/90

答

1/2+1/6+1/12+1/20+.........+1/90
=1-1/2+1/2-1/3+...+1/9-1/10
=1-1/10
=9/10

答

1/2+1/6+1/12+1/20+.+1/90
=1/1*2+1/2*3+1/3*4+1/4*5+...+1/9*10
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+...+1/9-1/10
=1-1/10
=9/10