(3x+3)(3x-6)=0

Solution for (3x+3)(3x-6)=0 equation:

(3x+3)(3x-6)=0

We multiply parentheses ..

(+9x^2-18x+9x-18)=0

We get rid of parentheses

9x^2-18x+9x-18=0

We add all the numbers together, and all the variables

9x^2-9x-18=0

a = 9; b = -9; c = -18;
Δ = b2-4ac
Δ = -92-4·9·(-18)
Δ = 729
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{729}=27$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-27}{2*9}=\frac{-18}{18}
=-1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+27}{2*9}=\frac{36}{18}
=2
$