Answer
the zeros are $$ x=\pm 2.$$
Work Step by Step
The zeros of $f(x)=x^2-4$ can be obtained by putting
$$x^2-4=0\Longrightarrow x=\pm 2.$$
Since $f(-x)=f(x)$ then the function is symmetric about the y-axis and increasing on the interval $(0,\infty)$ as in the figure below.
