Help with two functions

Vertex form of a parabola :

y = a(x-h)^2 +k

First one:    y = a (x-4)^2 -2     You are given a convenient point on the parabola to find 'a'

Let's sub 7,3  into the equation

3 = a (7-4)^2 -2      solve for a = 5/9

y = 5/9 (x-4)^2 -2