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

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

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

We multiply parentheses ..

x(-4x+20)=0

We multiply parentheses

-4x^2+20x=0

a = -4; b = 20; c = 0;
Δ = b2-4ac
Δ = 202-4·(-4)·0
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-20}{2*-4}=\frac{-40}{-8}
=+5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+20}{2*-4}=\frac{0}{-8}
=0
$