Answer
$ f(x)$ is continuous for all values of $ x $.
Work Step by Step
Since the third root (odd) is defined for all values of $ x $, the first term will be continuous. The same applies to the second term, which is a standard polynomial. The sum of two continuous functions is continuous. Hence, $$ f(x)=3x^{2/3}-9x^3$$
is continuous for all values of $ x $.
