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

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

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

We add all the numbers together, and all the variables

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

We multiply parentheses ..

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

We get rid of parentheses

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

We add all the numbers together, and all the variables

-20x^2+21x+5=0

a = -20; b = 21; c = +5;
Δ = b2-4ac
Δ = 212-4·(-20)·5
Δ = 841
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{841}=29$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-29}{2*-20}=\frac{-50}{-40}
=1+1/4
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+29}{2*-20}=\frac{8}{-40}
=-1/5
$