-5n(5n-8)=0

Solution for -5n(5n-8)=0 equation:

-5n(5n-8)=0

We multiply parentheses

-25n^2+40n=0

a = -25; b = 40; c = 0;
Δ = b2-4ac
Δ = 402-4·(-25)·0
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(40)-40}{2*-25}=\frac{-80}{-50}
=1+3/5
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(40)+40}{2*-25}=\frac{0}{-50}
=0
$