Question

1/6×9＋1/9×12＋1/12×15＋1/15×18＋1/18×21＋1/21×24(要用简便算法)

Answer 1

1/6×9＋1/9×12＋1/12×15＋1/15×18＋1/18×21＋1/21×24

=1/3(1/6-1/9)+1/3(1/9-1/12)+1/3(1/12-1/15)+1/3(1/15-1/18)

+1/3(1/18-1/21)+1/3(1/21-1/24)

=1/3(1/6-1/9+1/9-……+1/21-1/24)

=1/3(1/6-1/24)

=1/24