(x+6)(x-18)=0

Solution for (x+6)(x-18)=0 equation:

(x+6)(x-18)=0

We multiply parentheses ..

(+x^2-18x+6x-108)=0

We get rid of parentheses

x^2-18x+6x-108=0

We add all the numbers together, and all the variables

x^2-12x-108=0

a = 1; b = -12; c = -108;
Δ = b2-4ac
Δ = -122-4·1·(-108)
Δ = 576
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{576}=24$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-24}{2*1}=\frac{-12}{2}
=-6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+24}{2*1}=\frac{36}{2}
=18
$