(20-2x)(30-2x)=56

Solution for (20-2x)(30-2x)=56 equation:

(20-2x)(30-2x)=56

We move all terms to the left:

(20-2x)(30-2x)-(56)=0

We add all the numbers together, and all the variables

(-2x+20)(-2x+30)-56=0

We multiply parentheses ..

(+4x^2-60x-40x+600)-56=0

We get rid of parentheses

4x^2-60x-40x+600-56=0

We add all the numbers together, and all the variables

4x^2-100x+544=0

a = 4; b = -100; c = +544;
Δ = b2-4ac
Δ = -1002-4·4·544
Δ = 1296
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1296}=36$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-100)-36}{2*4}=\frac{64}{8}
=8
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-100)+36}{2*4}=\frac{136}{8}
=17
$