Use three different ways (graph, table, algebraically) to convince someone that...
a) If it is odd...it will be symmetric with the origin
See that this is so, here : https://www.desmos.com/calculator/jxqiwmmria
b) If it is odd we will hve the points (-x, -y) and (x , y) on the grpah
So by a table
c) If it is odd
f(-x) = - f(x)
f(-x) = (-x)^3 + 2(-x) = -x^3 - 2x = - [ x^2 + 2x ] = - f(x)