How to solve the square of x-6x-18 = 0 with the collocation method?

How to solve the square of x-6x-18 = 0 with the collocation method?

x^2-6x-18=0,
x^2-6x=18,
x^2-6x+9=18+9
(x-3)^2=27,
X-3 = √ 27 = 3 √ 3, or x-3 = - √ 27 = - 3 √ 3
X1 = 3 + 3 √ 3, or x2 = 3-3 √ 3

The square of X + 6x + 18 = 0. Solving x needs detailed process speed··
Solve X. who is the most detailed and who is the fastest

x²+6x+9+9=0
(x+3)²=-9
The square is greater than or equal to 0
So it's not equal to - 9
So the equation has no solution

To solve the system of equations (quadratic power of x-6x) + 18 (quadratic power of x-6x) + 81 = 0

(x^2-6x)^2+18(x^2-6x)+81=0
[(x^2-6x)+9]^2=0
(x^2-6x)+9=0
(x-3)^2=0
x-3=0
x=3