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

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

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

We multiply parentheses ..

5(+a^2-8a+2a-16)=0

We multiply parentheses

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

We add all the numbers together, and all the variables

5a^2-30a-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:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

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