Answer:
-4
Step-by-step explanation:
To find the x-coordinate of the vertex of a parabola given its x-intercepts, find the average of the x-intercepts:
x-coordinate of the vertex = [tex]\frac{x_1+x_2}{2}[/tex] (where [tex]x_1[/tex] and [tex]x_2[/tex] are the x-intercepts)
Plug in the x-intercepts 13 and -21
[tex]\frac{13+(-21)}{2}\\= \frac{13-21}{2}\\= \frac{-8}{2}\\=-4[/tex]
Therefore, the x-coordinate of the vertex is -4.
I hope this helps!
