Chapter 8 - Graphing Quadratic Functions - 8.2 - Graphing f(x) = ax^2 + c - Exercises - Page 429: 26

$x=\pm\frac{7}{2}$

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 $x$: $$f(x)=-8x^2+98$$ $$-8x^2+98=0$$ $$-8x^2=-98$$ $$x^2=\frac{98}{8}=\frac{49}{4}$$ $$x=\pm\sqrt{\frac{49}{4}}=\pm\frac{7}{2}$$