Exploring Parabola: Focus-Directrix Distance Equality

Exploring Parabola: Focus-Directrix Distance Equality
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2017-03-19 21:45
This GeoGebra example dynamically demonstrates the fundamental property of a parabola: any point on the parabola is equidistant from the focus and the directrix. The core mathematical concepts involved include parabola, focus, directrix, distance measurement, and geometric construction. The construction uses commands such as Line and Parabola to create the directrix and the parabola, Point to place a movable point on the curve, Intersect and OrthogonalLine to construct perpendicular projections, and Distance to compute the distances from the point to the focus and to the directrix. Text objects display these distances, allowing students to visually verify the equality as the point moves. This is suitable for high school analytic geometry or introductory college geometry courses, helping learners grasp the definition of a parabola and the geometric meaning of focus and directrix through interactive exploration.

GeoGebra Commands & Parameters

  1. Line(B, A) → f
  2. Parabola(C, f) → d
  3. Intersect(d, xAxis, 1) → D
  4. Distance(C, D) → distanceCD
  5. Distance(D, f) → distanceDf
  6. Point(d) → E
  7. Distance(E, C) → distanceEC
  8. Distance(E, f) → distanceEf
  9. Segment(C, E) → g
  10. OrthogonalLine(E, f) → h
  11. Intersect(h, f) → F
  12. Segment(E, F) → i
  13. Point(d) → G
  14. Point(d) → H
  15. Segment(G, H) → j