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

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

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

We use the square of the difference formula

x^2-(x+3)-9=0

We get rid of parentheses

x^2-x-3-9=0

We add all the numbers together, and all the variables

x^2-1x-12=0

a = 1; b = -1; c = -12;
Δ = b2-4ac
Δ = -12-4·1·(-12)
Δ = 49
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{49}=7$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-7}{2*1}=\frac{-6}{2}
=-3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+7}{2*1}=\frac{8}{2}
=4
$