(5x+5)(2x-8)=0

Solution for (5x+5)(2x-8)=0 equation:

(5x+5)(2x-8)=0

We multiply parentheses ..

(+10x^2-40x+10x-40)=0

We get rid of parentheses

10x^2-40x+10x-40=0

We add all the numbers together, and all the variables

10x^2-30x-40=0

a = 10; b = -30; c = -40;
Δ = b2-4ac
Δ = -302-4·10·(-40)
Δ = 2500
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2500}=50$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-50}{2*10}=\frac{-20}{20}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+50}{2*10}=\frac{80}{20}
=4
$