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

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

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

We multiply parentheses ..

(-20x^2-20x-25x-25)=0

We get rid of parentheses

-20x^2-20x-25x-25=0

We add all the numbers together, and all the variables

-20x^2-45x-25=0

a = -20; b = -45; c = -25;
Δ = b2-4ac
Δ = -452-4·(-20)·(-25)
Δ = 25
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{25}=5$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-45)-5}{2*-20}=\frac{40}{-40}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-45)+5}{2*-20}=\frac{50}{-40}
=-1+1/4
$