tìm x `x^2 - x - 2 = 0 `

`x^2-x-2=0`

`⇔x^2+x-2x-2=0`

`⇔x(x+1)-2(x+1)=0`

`⇔(x+1)(x-2)=0`

`⇔`\(\left[ \begin{array}{l}x+1=0\\x-2=0\end{array} \right.\) 

`⇔`\(\left[ \begin{array}{l}x=-1\\x=2\end{array} \right.\) 

Vậy `x={-1,2}`