(x-5)(x-4)=56

Solution for (x-5)(x-4)=56 equation:

(x-5)(x-4)=56

We move all terms to the left:

(x-5)(x-4)-(56)=0

We multiply parentheses ..

(+x^2-4x-5x+20)-56=0

We get rid of parentheses

x^2-4x-5x+20-56=0

We add all the numbers together, and all the variables

x^2-9x-36=0

a = 1; b = -9; c = -36;
Δ = b2-4ac
Δ = -92-4·1·(-36)
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-15}{2*1}=\frac{-6}{2}
=-3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+15}{2*1}=\frac{24}{2}
=12
$