The following Applet is to help see the geometric interpretation in 5.3.2 of the Binghamton University Course Math 108. Ultimately it is to help visualize the relation between the directrix and focus on that affect the shape of the parabola. Recall: The Equation of the Parabola is $f(x)=\frac{1}{4p}(x-h)^2 +k$ The Vertex is (h,k) The Focus is (h,p+k) [Coordinates can be changed using the sliders below] The Derectrix is y=-p+k [The y-value of this line can be changed using the sliders below]