f(x)=-3x^2+18-27

Question

in standard form

Answer 1

Do you mean f(x)=-3x²+18x-27?

If so, then this is the equation of a parabola. If, by standard form you mean in vertex form, then:

f(x)=-3(x²-6x+9)=-3(x-3)², where the vertex is at (3,0) and the vertex is a maximum turning-point, so the parabola is like an inverted narrow U with gradually spreading arms.