Tim x: x^2-12x+20=0.

`x^2 - 12x +20=0`

`x^2 - 10x - 2x +20=0`

`(x^2 - 10x) + (-2x +20)=0`

`x(x-10 ) - 2(x-10)=0`

`(x-10)(x-2)=0`

`=>`\(\left[ \begin{array}{l}x-10=0\\x-2=0\end{array} \right.\) 

`=>`\(\left[ \begin{array}{l}x=10\\x=2\end{array} \right.\) 

`\text{Vậy}  x∈{2;10}`