The real function f is an odd function if f(−x) = − f(x) for all x (in the domain of f). Thus the graph y = f(x) of an odd function has rotational symmetry of order 2 about the origin because whenever (x,y) lies on the graph then so does (−x,−y). The following are odd functions of x: 2x, x3, x7 − 8x3 + 5x, 1/(x3 − x), sin x, tan x.