(3x+9)(5x-5)=0

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

(3x+9)(5x-5)=0

We multiply parentheses ..

(+15x^2-15x+45x-45)=0

We get rid of parentheses

15x^2-15x+45x-45=0

We add all the numbers together, and all the variables

15x^2+30x-45=0

a = 15; b = 30; c = -45;
Δ = b2-4ac
Δ = 302-4·15·(-45)
Δ = 3600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3600}=60$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(30)-60}{2*15}=\frac{-90}{30}
=-3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(30)+60}{2*15}=\frac{30}{30}
=1
$