(20-2x)(26-2x)=315

Solution for (20-2x)(26-2x)=315 equation:

(20-2x)(26-2x)=315

We move all terms to the left:

(20-2x)(26-2x)-(315)=0

We add all the numbers together, and all the variables

(-2x+20)(-2x+26)-315=0

We multiply parentheses ..

(+4x^2-52x-40x+520)-315=0

We get rid of parentheses

4x^2-52x-40x+520-315=0

We add all the numbers together, and all the variables

4x^2-92x+205=0

a = 4; b = -92; c = +205;
Δ = b2-4ac
Δ = -922-4·4·205
Δ = 5184
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5184}=72$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-92)-72}{2*4}=\frac{20}{8}
=2+1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-92)+72}{2*4}=\frac{164}{8}
=20+1/2
$