Parabola Geometric Construction: Focus-Directrix Definition

Parabola Geometric Construction: Focus-Directrix Definition
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2019-05-23 00:15
This GeoGebra example demonstrates the geometric construction of a parabola based on its focus-directrix definition: the locus of points equidistant from a fixed point (focus F) and a fixed line (directrix). Core mathematical concepts include conic sections, focus, directrix, perpendicular bisector, midpoint, tangent, and locus. The construction uses commands such as Line, Point, Segment, Midpoint, OrthogonalLine, Intersect, and Locus. Steps: create focus F and directrix g, choose a moving point D on the directrix, draw the perpendicular from D to the directrix, connect D to F, take the midpoint M_1 of DF, construct the perpendicular bisector of DF, and intersect it with the perpendicular through D to obtain point P. The Locus command traces P to generate the parabola. Additional elements like tangents, segments FP and EP, and auxiliary points are included. Suitable for high school analytic geometry or introductory college conic sections, ideal for exploring tangent properties and geometric constructions.

GeoGebra Commands & Parameters

  1. Line(A, B) → f
  2. Point(f) → D
  3. Segment(D, F) → DF
  4. Midpoint(DF) → M_1
  5. OrthogonalLine(D, f) → perpendicular_{Directrix}
  6. OrthogonalLine(M_1, DF) → perpendicular_{DF}
  7. Intersect(perpendicular_{DF}, perpendicular_{Directrix}) → C
  8. Segment(C, D) → CD
  9. Segment(C, F) → CF
  10. Locus(C, D) → Parabola_{Locus}
  11. Point(Parabola_{Locus}) → P
  12. OrthogonalLine(P, f) → g
  13. Intersect(g, f) → E
  14. Segment(F, E) → EF
  15. Midpoint(EF) → M_2
  16. Line(M_2, P) → Tangent
  17. Segment(P, F) → FP
  18. Segment(P, E) → EP

AI Drawing Prompt Reference

Draw a parabola based on its focus-directrix definition: the locus of points equidistant from a fixed point (focus) and a fixed line (directrix). Start by plotting the focus and directrix, then choose a moving point on the directrix. Draw a perpendicular from this point to the directrix, connect the point to the focus, find the midpoint of the segment, construct the perpendicular bisector of the segment, and find its intersection with the perpendicular line to get a point on the parabola. Trace these points to form the parabola. Include the tangent line, segments from the focus to the tangent point, and from the directrix to the tangent point.
The prompt above was compiled from the original drawing commands and is for reference only.