Tính nhanh 20/5×7+20/7×9+20/9×11+20/11×13+……+20/33×35

0 bình luận về “Tính nhanh 20/5×7+20/7×9+20/9×11+20/11×13+……+20/33×35”

1. `20/(5xx7)+20/(7xx9)+20/(9xx11)+20/(11xx13)+…+20/(33xx35)`

   `=10(2/(5xx7)+2/(7xx9)+2/(9xx11)+2/(11xx13)+…+2/(33xx35))`

   `=10(1/(5)-1/7+1/7-1/9+1/9-1/11+1/11-1/13+…+1/33-1/35)`

   `=10(1/5-1/35)`

   `=10*6/35`

   `=12/7`

   Bình luận