An equation must be stated as something is equal to something. A function would be given a name and then equated to an expression. The polynomial alone as given is not enough. Do you want the function, or do you want the quadratic expression equal to 0 or some constant?
The given expression appears to be for a circle. Is the expression equal to 0?
Best guess,
which would be a circle centered at the origin, with radius 6 units.