-4(x+2)(x-18)=0

Solution for -4(x+2)(x-18)=0 equation:

-4(x+2)(x-18)=0

We multiply parentheses ..

-4(+x^2-18x+2x-36)=0

We multiply parentheses

-4x^2+72x-8x+144=0

We add all the numbers together, and all the variables

-4x^2+64x+144=0

a = -4; b = 64; c = +144;
Δ = b2-4ac
Δ = 642-4·(-4)·144
Δ = 6400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{6400}=80$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(64)-80}{2*-4}=\frac{-144}{-8}
=+18
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(64)+80}{2*-4}=\frac{16}{-8}
=-2
$