A parabola has zeros at x=-2 and x=8. What is the x-coordinate of the vertex of the parabola?

A parabola is symmetric about its axis, which passes through the vertex. The axis is exactly halfway between the two zeros, so the vertex's $x$-coordinate is the average of $-2$ and $8$: $\frac{-2 + 8}{2} = 3$, choice D. Choice A (6) is the sum of the zeros. Choice B (5) is half the distance between the zeros, $\frac{8-(-2)}{2}$, which gives the half-width of the parabola, not the position of its center. Choice C ($-5$) comes from a sign error with that half-distance. Add the zeros and divide by 2.