Tính nhanh a) (a × 7 + a × 8 - a × 15) : ( 1 + 2 + 3 + ........ + 10)
Giải thích
a) (a × 7 + a × 8 - a × 15) : ( 1 + 2 + 3 + ........ + 10)
= a × (7 + 8 – 15) : ( 1 + 2 + 3 + ........ + 10)
= (a × 0) : ( 1 + 2 + 3 + ........ + 10)
= 0 : ( 1 + 2 + 3 + ........ + 10)
= 0