800=x(x+1)

Solution for 800=x(x+1) equation:

800=x(x+1)

We move all terms to the left:

800-(x(x+1))=0


We calculate terms in parentheses: -(x(x+1)), so:

x(x+1)

We multiply parentheses

x^2+x

Back to the equation:

-(x^2+x)


We get rid of parentheses

-x^2-x+800=0

We add all the numbers together, and all the variables

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

a = -1; b = -1; c = +800;
Δ = b2-4ac
Δ = -12-4·(-1)·800
Δ = 3201
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-\sqrt{3201}}{2*-1}=\frac{1-\sqrt{3201}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{3201}}{2*-1}=\frac{1+\sqrt{3201}}{-2}
$