Even Function - Symmetry about the Vertical Axis
A function, f, is symmetrical about the vertical axis when all the values of x in the domain are verified:
f(−x) = f(x)
The functions that are symmetrical about the vertical axis are called even functions.
Odd Function - Symmetry about the Origin
A function, f, is symmetrical about the origin if all values of x in the domain are verified:
f(−x) = −f(x)
The symmetrical functions about the origin are called odd functions.