## Quick Reference

The real function *f* is an even function if *f*(−*x*)=*f*(*x*) for all *x* (in the domain of *f*). Thus the graph *y*=*f*(*x*) of an even function has the *y*-axis as a line of symmetry. For example, *f* is an even function when *f*(*x*) is defined as any of the following: 5, *x*^{2}, *x*^{6}−4*x*^{4}+1, 1/(*x*^{2}−3), cos *x*.

*Subjects:*
Mathematics.