10a(20-4a)=0

Solution for 10a(20-4a)=0 equation:

10a(20-4a)=0

We add all the numbers together, and all the variables

10a(-4a+20)=0

We multiply parentheses

-40a^2+200a=0

a = -40; b = 200; c = 0;
Δ = b2-4ac
Δ = 2002-4·(-40)·0
Δ = 40000
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{40000}=200$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(200)-200}{2*-40}=\frac{-400}{-80}
=+5
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(200)+200}{2*-40}=\frac{0}{-80}
=0
$