Find the zeros of the function f(x) = x2+ 6x + 18. the 2 is square

To find the number of zeros in the quadratic equation we factorize it as follows:
f(x)=x²+6x+18
solving using completing square methods we obtain:
x^2+6x=-18
c=(b/2a)^2=9
thus
x²+6x+9=-18+8
x²+6x+9=-9
(x+3)²=-9
hence
x=-3+/-3i
the roots are:
x=-3+3i or x=-3-3i