A cubic function is a polynomial function that has a degree of 3. y=ax^3+bx^2+cx+d Here, a, b, c and d are real numbers and a ≠ 0. The parent function is y=x^3 and depending on the values of the coefficients, cubic functions have different shapes. A cubic function can have a relative minimum and maximum — the highest and lowest point for a region of its graph. The domain and range of a cubic function are all real numbers.