-5n(4n-9)=0

Solution for -5n(4n-9)=0 equation:

-5n(4n-9)=0

We multiply parentheses

-20n^2+45n=0

a = -20; b = 45; c = 0;
Δ = b2-4ac
Δ = 452-4·(-20)·0
Δ = 2025
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2025}=45$
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(45)-45}{2*-20}=\frac{-90}{-40}
=2+1/4
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(45)+45}{2*-20}=\frac{0}{-40}
=0
$