(100-2x)(80-2x)=0

Solution for (100-2x)(80-2x)=0 equation:

(100-2x)(80-2x)=0

We add all the numbers together, and all the variables

(-2x+100)(-2x+80)=0

We multiply parentheses ..

(+4x^2-160x-200x+8000)=0

We get rid of parentheses

4x^2-160x-200x+8000=0

We add all the numbers together, and all the variables

4x^2-360x+8000=0

a = 4; b = -360; c = +8000;
Δ = b2-4ac
Δ = -3602-4·4·8000
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-360)-40}{2*4}=\frac{320}{8}
=40
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-360)+40}{2*4}=\frac{400}{8}
=50
$