18=2x*x

Solution for 18=2x*x equation:

18=2x*x

We move all terms to the left:

18-(2x*x)=0

We add all the numbers together, and all the variables

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

We get rid of parentheses

-2x*x+18=0

Wy multiply elements

-2x^2+18=0

a = -2; b = 0; c = +18;
Δ = b2-4ac
Δ = 02-4·(-2)·18
Δ = 144
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{144}=12$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-12}{2*-2}=\frac{-12}{-4}
=+3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+12}{2*-2}=\frac{12}{-4}
=-3
$