800=(x+20)*x

Solution for 800=(x+20)*x equation:

800=(x+20)*x

We move all terms to the left:

800-((x+20)*x)=0


We calculate terms in parentheses: -((x+20)*x), so:

(x+20)*x

We multiply parentheses

x^2+20x

Back to the equation:

-(x^2+20x)


We get rid of parentheses

-x^2-20x+800=0

We add all the numbers together, and all the variables

-1x^2-20x+800=0

a = -1; b = -20; c = +800;
Δ = b2-4ac
Δ = -202-4·(-1)·800
Δ = 3600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3600}=60$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-60}{2*-1}=\frac{-40}{-2}
=+20
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+60}{2*-1}=\frac{80}{-2}
=-40
$