(18-2x)(26-2x)=128

Solution for (18-2x)(26-2x)=128 equation:

(18-2x)(26-2x)=128

We move all terms to the left:

(18-2x)(26-2x)-(128)=0

We add all the numbers together, and all the variables

(-2x+18)(-2x+26)-128=0

We multiply parentheses ..

(+4x^2-52x-36x+468)-128=0

We get rid of parentheses

4x^2-52x-36x+468-128=0

We add all the numbers together, and all the variables

4x^2-88x+340=0

a = 4; b = -88; c = +340;
Δ = b2-4ac
Δ = -882-4·4·340
Δ = 2304
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2304}=48$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-88)-48}{2*4}=\frac{40}{8}
=5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-88)+48}{2*4}=\frac{136}{8}
=17
$