(2x-6)(4x+20)=0

Solution for (2x-6)(4x+20)=0 equation:

(2x-6)(4x+20)=0

We multiply parentheses ..

(+8x^2+40x-24x-120)=0

We get rid of parentheses

8x^2+40x-24x-120=0

We add all the numbers together, and all the variables

8x^2+16x-120=0

a = 8; b = 16; c = -120;
Δ = b2-4ac
Δ = 162-4·8·(-120)
Δ = 4096
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4096}=64$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-64}{2*8}=\frac{-80}{16}
=-5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+64}{2*8}=\frac{48}{16}
=3
$