What is the range of the function f(x) = 3x2 + 6x – 9

I have a solution here however with a slight change in the equation:

 f(x)=3x^2-6x+1

My solution is:

The domain is all real numbers--there are no restrictions like a square root or variable in the denominator 

this is a U shape parabola and you want to find the bottom point, it is at the vertex 
x=-b/2a =- (-6) /2 (3) =1 
f(1) =3(1)^2 -6(1) +1 =3-6+1 =-2 
the minimum is (1, -2) 
so the range is all real numbers >= -2

By examining my solution, you could just answer the problem on your own! I hope it helps!