Consider the graph of the following quadratic equation. the equation of the quadratic function represented by the graph is y = a(x-3)^2 -1. what is the value of a?

For x values 1 unit either side of the vertex, the value of y is 2 more than it is at the vertex.
  a = 2


More formally, The graph appears to go through the point (4, 1). Substituting these values for (x, y) in the equation, we get
  1 = a(4-3)² -1 . . . . substitute for x and y
  2 = a . . . . . . . . . . add 1 and simplify