(40-2x)(60-2x)=800

Solution for (40-2x)(60-2x)=800 equation:

(40-2x)(60-2x)=800

We move all terms to the left:

(40-2x)(60-2x)-(800)=0

We add all the numbers together, and all the variables

(-2x+40)(-2x+60)-800=0

We multiply parentheses ..

(+4x^2-120x-80x+2400)-800=0

We get rid of parentheses

4x^2-120x-80x+2400-800=0

We add all the numbers together, and all the variables

4x^2-200x+1600=0

a = 4; b = -200; c = +1600;
Δ = b2-4ac
Δ = -2002-4·4·1600
Δ = 14400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{14400}=120$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-200)-120}{2*4}=\frac{80}{8}
=10
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-200)+120}{2*4}=\frac{320}{8}
=40
$