$$ 2x^2 -12=3x \quad | -3x $$
$$ 2x^2-3x-12=0 $$
$$ x^2 -(3/2)x -6 = 0 $$
Anwenden der PQ Formel
$$ p=-3/2 \quad q=-6 $$
$$ \frac{-p}{2}\pm \sqrt{\left(\frac{p}{2}\right)^2-q} $$
$$ x_1 = -1.8117... \quad x_2 =3.3117 $$
~plot~ 2x^2-3x-12 ~plot~
Hope this helps!