Tìm x biết:
(x+3)-2x2-12x-18=0
<=> (x+3)-2(x2+6x+9)=0
<=> (x+3)-2(x+3)2=0
<=> (x+3)\(\left[1-2\left(x+3\right)\right]\)=0
<=> (x+3)(2x+5)=0
<=> 2x2+5x+6x+15=0
<=>2x2+11x+15=0
<=> \(\left[\begin{array}{} x=\dfrac{-5}{2}\\ x=-3 \end{array} \right.\)