(4x+8)(5x-5)=0

Solution for (4x+8)(5x-5)=0 equation:

(4x+8)(5x-5)=0

We multiply parentheses ..

(+20x^2-20x+40x-40)=0

We get rid of parentheses

20x^2-20x+40x-40=0

We add all the numbers together, and all the variables

20x^2+20x-40=0

a = 20; b = 20; c = -40;
Δ = b2-4ac
Δ = 202-4·20·(-40)
Δ = 3600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3600}=60$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-60}{2*20}=\frac{-80}{40}
=-2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+60}{2*20}=\frac{40}{40}
=1
$