How to find "a"???
Pick a point on the graph other than the vertex. Let's say you see the line pass through (1,5) and the vertex is at (3,4)...
First the vertex gives you this...
y = a (x - 3)2 + 4
Put the values (1,5) into this equation.
5 = a (1 - 3)2 + 4
Solve for a
5 = a*(-2)2 + 4
5 = 4a + 4
1 = 4a
1/4 = a
Final equation is
y = 1/4*(x - 3)2 + 4
