Answer
$${\text{False}}$$
Work Step by Step
$$\eqalign{
& {\text{Counterexample}} \cr
& {\text{Let }}y = \sqrt {{x^2} + 1} ,{\text{ this is not a rational function}} \cr
& {\text{Differentiate with respect to }}x \cr
& \frac{{dy}}{{dx}} = \frac{d}{{dx}}\left[ {\sqrt {{x^2} + 1} } \right] \cr
& \frac{{dy}}{{dx}} = \frac{{2x}}{{2\sqrt {{x^2} + 1} }} \cr
& \frac{{dy}}{{dx}} = \frac{x}{{\sqrt {{x^2} + 1} }},{\text{ this is a rational function}} \cr
& {\text{Therefore,}} \cr
& {\text{The statement is false}} \cr} $$