Answer
$$ f(x)=0.$$
Work Step by Step
Recall that an even function must satisfy: $f(-x)=f(x)$
Recall that an odd function must satisfy: $f(-x)=-f(x)$
The only function that is both even and odd is the zero function $$ f(x)=0.$$
We can see that:
$f(-x)=f(x)=-f(x)=0$
