There are several ways to write the equation. It depends on how you decide to draw the x- and y-axes.
The y-axis could go through the point where the water leaves the hose at (0, 4). On the other hand you could put the y-axis through the vertex and place the x-axis so that the nozzle is at (−4, 0). Still another possibility is to make the vertex the point (0, 0).
Use the general equation of a parabola in graphing form: y = a(x − h)2 + k
After you've filled in the values for h and k, you will need to substitute one point (x, y) in order to solve for a. Then you will be able to write the equation.
Use the eTool below to check your work.
Click the link at right for the full version of the eTool: A2C 4-64 HW eTool