(5x-20)(6x+3)=0

Solution for (5x-20)(6x+3)=0 equation:

(5x-20)(6x+3)=0

We multiply parentheses ..

(+30x^2+15x-120x-60)=0

We get rid of parentheses

30x^2+15x-120x-60=0

We add all the numbers together, and all the variables

30x^2-105x-60=0

a = 30; b = -105; c = -60;
Δ = b2-4ac
Δ = -1052-4·30·(-60)
Δ = 18225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{18225}=135$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-105)-135}{2*30}=\frac{-30}{60}
=-1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-105)+135}{2*30}=\frac{240}{60}
=4
$