`(x-7)( x^2 - 4 ) = 0`

`<=>` $\left[\begin{matrix} x - 7 = 0 \\ x^2 - 4 = 0 \end{matrix}\right.$

`<=>` $\left[\begin{matrix} x = 7 \\ x^2 = 4 \end{matrix}\right.$

`<=> $\left[\begin{matrix} x = 7 \\ x = \pm 2 \end{matrix}\right.$

vậy `S={` $\pm$2 `;7}`

`@Tobi`