You need to label the polynomial as follows: f(x) = 2-5x^3+6x.
Next, rearrange the terms in descending powers of x:
f(x) = -5x^3 + 6x + 2. The coefficient of the x^2 term is zero (0).
This definitely is a polynomial, but not a fourth degree one.
Because the highest power of x is 3 (as in x^3), this is a polynomial, a cubic trinomial (it has 3 terms).
