`=> 3x^4 + 9x^3 - 3x^2 - 3x^4 + 3x^3 - 9x^3 + 12 = 3x^2 + 3x^3 + 6x`
`<=> (3x^4 - 3x^4) + (9x^3 + 3x^3 - 9x^3 - 3x^3) + (-3x^2 - 3x^2) - 6x + 12 = 0`
`<=> -6x^2 - 6x + 12 = 0`
`=> x^2 + x - 2 = 0`
`=> (x-1)(x+2) = 0`
`=> x = 1` hoặc `x = -2`.
`3x^2(x^2+3x-1)-3x(x^3-x^2)-9x^3+12=3x^2+3x^3+6x`
`<=>3x^4+9x^3-3x^2-3x^4+3x^3-9x^3+12=3x^2+3x^3+6x`
`<=>6x^2+6x-12=0`
`<=>x^2+x-2=0`
`<=>x^2+2x-x-2=0`
`<=>x(x+2)-(x+2)=0`
`<=>(x+2)(x-1)=0`
`<=>` $\left[\begin{matrix} x=-2\\ x=1\end{matrix}\right.$
Vậy `S={-2;1}`
\(3x^2\left(x^2+3x-1\right)-3x\left(x^3-x^2\right)+12=3x^2+3x^3+6x\)
\(\Leftrightarrow3x^4+9x^3-3x^2-3x^4+3x^3+12-3x^2-3x^3-6x=0\)
\(\Leftrightarrow-6x^2-6x+12=0\)
\(\Leftrightarrow x^2+x-2=0\)
\(\Leftrightarrow x^2+2x-x-2=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=1\end{matrix}\right.\)
Vậy \(S=\left\{-2;1\right\}\)
`3x^2(x^2+3x-1)-3x(x^3-x^2)-9x^3+12=3x^2+3x^3+6x`
`<=>3x^4+9x^3-3x^2-3x^4+3x^3-9x^3+12=3x^2+3x^3+6x`
`<=>-3x^2+3x^3+12=3x^2+3x^3+6x`
`<=>-3x^2+3x^3-3x^2-3x^3-6x=-12`
`<=>-6x=-12`
`<=>x=-12/-6=2`
