18+x=x*x-x*2

Solution for 18+x=x*x-x*2 equation:

18+x=x*x-x*2

We move all terms to the left:

18+x-(x*x-x*2)=0

We add all the numbers together, and all the variables

x-(+x*x-x*2)+18=0

We get rid of parentheses

x-x*x+x*2+18=0

Wy multiply elements

-1x^2+x+2x+18=0

We add all the numbers together, and all the variables

-1x^2+3x+18=0

a = -1; b = 3; c = +18;
Δ = b2-4ac
Δ = 32-4·(-1)·18
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(3)-9}{2*-1}=\frac{-12}{-2}
=+6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3)+9}{2*-1}=\frac{6}{-2}
=-3
$