Question 982199
Does y have a maximum or a minimum value?


{{{y=ax^2}}} is a parabola, concave upward if {{{a>0}}}, and concave downward if {{{a<0}}}.


Your equation IS NOT a parabola.
Be aware, your equation may have more than two local extreme values.


One would guess you want to use Rational Roots Theorem to look for those roots. (Maybe use of substitution for x^3, because your equation is in "quadratic form", but it is not a parabola.)