(x+9)(x+3)=396

Solution for (x+9)(x+3)=396 equation:

(x+9)(x+3)=396

We move all terms to the left:

(x+9)(x+3)-(396)=0

We multiply parentheses ..

(+x^2+3x+9x+27)-396=0

We get rid of parentheses

x^2+3x+9x+27-396=0

We add all the numbers together, and all the variables

x^2+12x-369=0

a = 1; b = 12; c = -369;
Δ = b2-4ac
Δ = 122-4·1·(-369)
Δ = 1620
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1620}=\sqrt{324*5}=\sqrt{324}*\sqrt{5}=18\sqrt{5}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-18\sqrt{5}}{2*1}=\frac{-12-18\sqrt{5}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+18\sqrt{5}}{2*1}=\frac{-12+18\sqrt{5}}{2}
$