Tính A = 999994 . 999999 . 999992 – 999996 . 999991 . 999998

Giải thích các bước giải:

`A=999994.999999.999992−999996.999991.999998`

Đặt `a=999999`

`=>A=(a−5)a(a−7)−(a−3)(a−8)(a−1)`

`=a^2−5a(a−7)−(a^2−3a−8a+24)(a−1)`

`=a^3−7a^2−5a^2+35a−a^3+3a^2+8a^2−24a+a^2−3a−8a+24`

`=24`

Vậy` A=24`