用简便方法计算:1/2+1/6+1/12+1/20+…+1/90

Answer 1

1/2+1/6+1/12+1/20+…+1/90
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1-1/10
=9/10（10分之9）
朋友，请【采纳答案】，您的采纳是我答题的动力，谢谢。

Answer 2

1/2+1/6+1/12+1/20+…+1/90
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1-1/10
=9/10（10分之9）

Answer 3

1-90/1=90/89