-5(y-3)(-y-9)=0

Solution for -5(y-3)(-y-9)=0 equation:

-5(y-3)(-y-9)=0

We add all the numbers together, and all the variables

-5(y-3)(-1y-9)=0

We multiply parentheses ..

-5(-1y^2-9y+3y+27)=0

We multiply parentheses

5y^2+45y-15y-135=0

We add all the numbers together, and all the variables

5y^2+30y-135=0

a = 5; b = 30; c = -135;
Δ = b2-4ac
Δ = 302-4·5·(-135)
Δ = 3600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3600}=60$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(30)-60}{2*5}=\frac{-90}{10}
=-9
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(30)+60}{2*5}=\frac{30}{10}
=3
$