Answer
$y = \frac{3}{10}x^2 − \frac{6}{5}$
Work Step by Step
Let $y = ax2 + bx + c$.
Substitute the point $(2, 0)$ gives the equation;
$4a + 2b + c = 0$
Substitute the point $(8,18)$ gives the equation;
$64a + 8b + c = 18$
Substitute the point $(-8, 18)$ gives the equation;
$64a − 8b + c = 18$,
Now solving for $a$, $b$ and $c$ from the equations above gives us $a = \frac{3}{10}$, $b = 0$ and $c = -\frac{6}{5}$
Hence $y = \frac{3}{10}x^2 − \frac{6}{5}$
