This iss sort of related to my previous post about my Mock Exam paper, anyway, was going through my notes and I found what I think is a similar example to what I orginally Posted. Again, Im stuck and can't do it, can anybody point me in the right direction.

There exists a function $\displaystyle f(x) = x^3$ where $\displaystyle x \in Q$

Show that the function, f, is not continuous at x if $\displaystyle x \ne 0$