x ( x + 2 ) - 3 ( x + 2 ) = 0

`x(x+2)-3(x+2)=0`

`⇒x^{2}+2x-3x-6=0`

`⇒x^{2}-x-6=0`

`⇒(x^{2}-4)-(x+2)=0`

`⇒(x^{2}-2^{2})-(x+2)=0`

`⇒(x-2)(x+2)-(x+2)=0`

`⇒(x+2)(x-3)=0`

⇒\(\left[ \begin{array}{l}x+2=0\\x-3=3\end{array} \right.\) 

\(\left[ \begin{array}{l}x=-2\\x=3\end{array} \right.\)

Vậy `x∈{-2;3}`