(15x+45)(20x-100)=0

Solution for (15x+45)(20x-100)=0 equation:

(15x+45)(20x-100)=0

We multiply parentheses ..

(+300x^2-1500x+900x-4500)=0

We get rid of parentheses

300x^2-1500x+900x-4500=0

We add all the numbers together, and all the variables

300x^2-600x-4500=0

a = 300; b = -600; c = -4500;
Δ = b2-4ac
Δ = -6002-4·300·(-4500)
Δ = 5760000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5760000}=2400$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-600)-2400}{2*300}=\frac{-1800}{600}
=-3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-600)+2400}{2*300}=\frac{3000}{600}
=5
$