\begin{array}{c}\color{#003366}{-Gw}\color{#005A9C}{en}\color{#007ACC}{St}\color{#00AEEF}{ac}\color{#00CFFF}{y}\color{#A4D3EE}{-}\color{#D3D3D3}{}\color{#E0E0E0}{}\end{array} 

Bài `6`:

`P = -3x + 1/2x^3 - 3 - 1/2x^3 + x^2 + 2 - 4x^2`

`= 1/2x^3 - 1/2x^3 + x^2 - 4x^2 - 3x -3 + 2`

`= -3x^2 - 3x - 1`

`a)` Bậc: `2`

`-` Hệ số cao nhất: `-3`

`-` Hệ số tự do: `-1`

`b)` Khi `x = -2`

`P = -3.-2^2 + 6 - 1`

`= -12 + 6 - 1`

`= -6 - 1`

`= -7`

`c) -3x^2 - 3x - 1 = 0`

`3x^2 + 3x + 1 = 0`

`3(x^2 + x + 1/3) = 0`

`3(x + 1/2)^2 + 1/4 = 0`

`3(x + 1/2)^2 = -1/4`

`=>` Vô lý

`=>` PT vô nghiệm.