3x(x-4)=18

Solution for 3x(x-4)=18 equation:

3x(x-4)=18

We move all terms to the left:

3x(x-4)-(18)=0

We multiply parentheses

3x^2-12x-18=0

a = 3; b = -12; c = -18;
Δ = b2-4ac
Δ = -122-4·3·(-18)
Δ = 360
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{360}=\sqrt{36*10}=\sqrt{36}*\sqrt{10}=6\sqrt{10}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-6\sqrt{10}}{2*3}=\frac{12-6\sqrt{10}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+6\sqrt{10}}{2*3}=\frac{12+6\sqrt{10}}{6}
$