216=4x^2+12x

Solution for 216=4x^2+12x equation:

216=4x^2+12x

We move all terms to the left:

216-(4x^2+12x)=0

We get rid of parentheses

-4x^2-12x+216=0

a = -4; b = -12; c = +216;
Δ = b2-4ac
Δ = -122-4·(-4)·216
Δ = 3600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3600}=60$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-60}{2*-4}=\frac{-48}{-8}
=+6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+60}{2*-4}=\frac{72}{-8}
=-9
$