Question

1/1×5+1/5×9+1/9×13+1/13×17+1/17×21简便算法

Answer 1

原式=1/1-1/5+1/5-1/9+1/9-1/13+1/13-1/17-1/21 =1/1-1/21 =20/21 答案是21分之20 满意望采纳，谢谢。