(8-2x)(10-2x)=80

Solution for (8-2x)(10-2x)=80 equation:

(8-2x)(10-2x)=80

We move all terms to the left:

(8-2x)(10-2x)-(80)=0

We add all the numbers together, and all the variables

(-2x+8)(-2x+10)-80=0

We multiply parentheses ..

(+4x^2-20x-16x+80)-80=0

We get rid of parentheses

4x^2-20x-16x+80-80=0

We add all the numbers together, and all the variables

4x^2-36x=0

a = 4; b = -36; c = 0;
Δ = b2-4ac
Δ = -362-4·4·0
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{-(-36)-36}{2*4}=\frac{0}{8}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-36)+36}{2*4}=\frac{72}{8}
=9
$