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

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

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

We add all the numbers together, and all the variables

-5(u+2)(-1u+8)=0

We multiply parentheses ..

-5(-1u^2+8u-2u+16)=0

We multiply parentheses

5u^2-40u+10u-80=0

We add all the numbers together, and all the variables

5u^2-30u-80=0

a = 5; b = -30; c = -80;
Δ = b2-4ac
Δ = -302-4·5·(-80)
Δ = 2500
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2500}=50$
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-50}{2*5}=\frac{-20}{10}
=-2
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+50}{2*5}=\frac{80}{10}
=8
$