(x+13)(x-9)=168

Solution for (x+13)(x-9)=168 equation:

(x+13)(x-9)=168

We move all terms to the left:

(x+13)(x-9)-(168)=0

We multiply parentheses ..

(+x^2-9x+13x-117)-168=0

We get rid of parentheses

x^2-9x+13x-117-168=0

We add all the numbers together, and all the variables

x^2+4x-285=0

a = 1; b = 4; c = -285;
Δ = b2-4ac
Δ = 42-4·1·(-285)
Δ = 1156
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1156}=34$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(4)-34}{2*1}=\frac{-38}{2}
=-19
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4)+34}{2*1}=\frac{30}{2}
=15
$