Since the vertex of and a point on the parabola are given, we use the vertex form of a parabolic equation, or, with (h, k) being the vertex, and the point (x, y)
----- Substituting y for f(x), and then 0 for y, (1, 3) for (h, k), and (- 2, 0) for (x, y) in order to determine "a."
0 = 9a + 3
- 3 = 9a_____
------- Substituting for "a," and (1, 3) for (h, k)