-4(u-5)(-u-4)=0

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

-4(u-5)(-u-4)=0

We add all the numbers together, and all the variables

-4(u-5)(-1u-4)=0

We multiply parentheses ..

-4(-1u^2-4u+5u+20)=0

We multiply parentheses

4u^2+16u-20u-80=0

We add all the numbers together, and all the variables

4u^2-4u-80=0

a = 4; b = -4; c = -80;
Δ = b2-4ac
Δ = -42-4·4·(-80)
Δ = 1296
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1296}=36$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-36}{2*4}=\frac{-32}{8}
=-4
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+36}{2*4}=\frac{40}{8}
=5
$