-5(y-9)(-y-1)=0

Solution for -5(y-9)(-y-1)=0 equation:

-5(y-9)(-y-1)=0

We add all the numbers together, and all the variables

-5(y-9)(-1y-1)=0

We multiply parentheses ..

-5(-1y^2-1y+9y+9)=0

We multiply parentheses

5y^2+5y-45y-45=0

We add all the numbers together, and all the variables

5y^2-40y-45=0

a = 5; b = -40; c = -45;
Δ = b2-4ac
Δ = -402-4·5·(-45)
Δ = 2500
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2500}=50$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-40)-50}{2*5}=\frac{-10}{10}
=-1
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-40)+50}{2*5}=\frac{90}{10}
=9
$