Chapter 8 - Graphing Quadratic Functions - 8.2 - Graphing f(x) = ax^2 + c - Exercises - Page 429: 23

$x=\pm2$

The zeros of the function are the $x$-intercepts of this function. The $x$-intercepts can be found by equating the function expression to $0$ and solving for $x$: $$f(x)=4x^2-16$$ $$4x^2-16=0$$ $$4x^2=16$$ $$x^2=4$$ $$x=\pm\sqrt{4}=\pm2$$