Given the following function

graph the three functions **y = f(x), y = f(-x),** and **y = -f(-x)** and see if any two of the graphs coincide.

Using

> f:= x -> sin(x)+4*x^3;

> plot({f(x),f(-x)}, x=-1..1);

> plot({f(x),-f(-x)}, x=-1..1);

It appears from the latter graph that the two functions **y = f(x)** and
**y = -f(-x)** are the same. Hence, it appears that the function **y = f(x)** is odd.