(5-y)(5y+4)=0

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

(5-y)(5y+4)=0

We add all the numbers together, and all the variables

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

We multiply parentheses ..

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

We get rid of parentheses

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

We add all the numbers together, and all the variables

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

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

$\sqrt{\Delta}=\sqrt{841}=29$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-29}{2*-5}=\frac{-50}{-10}
=+5
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+29}{2*-5}=\frac{8}{-10}
=-4/5
$