I have a review problem I am having problems with. This is the problem:

Be able to show the function, g(x) is O(f(x)) numerically as we have done in class

Use the definition of O-notation to prove that 2x^2+3x+4 is O(x^2) (Do not use the theorem on polynomial orders)

This is what I have so far.
2x^2+3x+4 <= ax^2

(2x^2 is of the highest order in this problem)

(2x^2+3x+4)/ax^2 <=1 = 2x^2/ax^2 = 2/a

Then my prof said to let a=3 because it is larger than two. I am not sure where to go to from there.