(x-9)(x+4)=168

Solution for (x-9)(x+4)=168 equation:

(x-9)(x+4)=168

We move all terms to the left:

(x-9)(x+4)-(168)=0

We multiply parentheses ..

(+x^2+4x-9x-36)-168=0

We get rid of parentheses

x^2+4x-9x-36-168=0

We add all the numbers together, and all the variables

x^2-5x-204=0

a = 1; b = -5; c = -204;
Δ = b2-4ac
Δ = -52-4·1·(-204)
Δ = 841
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{841}=29$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-5)-29}{2*1}=\frac{-24}{2}
=-12
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-5)+29}{2*1}=\frac{34}{2}
=17
$