Consider the function \( f : R \rightarrow R \) defined by . Then \( f \) is :
monotonic on \( (-\infty, 0) \) only
monotonic on \( (-\infty, 0) \cup (0, \infty) \)
monotonic on \( (0, \infty) \) only
not monotonic \( (-\infty, 0) \) and \( (0, \infty) \)