The teacher will graph a horizontal line and plot a point using TI-Navigator™, and the class will provide the points that create a parabola.
Before the Activity
While using the TI-Navigator™ Activity Center for graphing and equation, the teacher graphs the line y = -3. Additionally, the teacher plots the point (0,-3). I recommend setting the coordinate increment at .25.
During the Activity
Once the line (directrix) and the point (focus) are visible on the graph, the teacher asks the students to plot a point that is located equidistant to the line (at a perpendicular distance) and the point.
Each student has to choose a different point, and these will be the students' best estimates.
With a little bit of luck and coaching, the points will begin to form the appearance of a parabola.
After the Activity
After activity is complete, have students try to estimate the equation of the parabola.
Continue this activity using different directrix and focus pairs, preferably ones that will not have a vertex at the origin.