(5n+1)(5n-4)=0

Solution for (5n+1)(5n-4)=0 equation:

(5n+1)(5n-4)=0

We multiply parentheses ..

(+25n^2-20n+5n-4)=0

We get rid of parentheses

25n^2-20n+5n-4=0

We add all the numbers together, and all the variables

25n^2-15n-4=0

a = 25; b = -15; c = -4;
Δ = b2-4ac
Δ = -152-4·25·(-4)
Δ = 625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{625}=25$
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-25}{2*25}=\frac{-10}{50}
=-1/5
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+25}{2*25}=\frac{40}{50}
=4/5
$