How do you figure out the equation of a parabola given a graph?

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Rachel -Assuming the parabola opens either up or down, the general formula is:Look at the graph and find the x-y coordinates of the vertex.  Insert the values in the formula above as follows:Vertex = (x,y) = (h,k)For example, if your vertex is (3,-2), then the equation becomes:Are you with me so far?  Great!So, now you only need to find the value of "a".  Do this by finding one more x-y point on the parabola.  Insert those x-y values into your equation and solve for a.  NOTE: If the parabola opens upward, then the value of "a" is positive, otherwise it is negative.Hope that helps