Final answer:
The formula describes y as a function of x because for any value of x, the polynomial equation will output only one corresponding value of y.
Step-by-step explanation:
The formula in question describes y as a function of x. A function is defined as a relation between a set of inputs and a set of permissible outputs with the property that each input is related to exactly one output. In this case, for any value of x, there is only one corresponding value of y. The given equation is a polynomial and it satisfies the definition of a function because for any input x, we can apply the equation to find a single resultant y value.