Parabola Locus: Construction with Tangents

Parabola Locus: Construction with Tangents
Loading the math board and drawing, please wait…
2020-09-08 13:47
This example demonstrates how to build and verify the locus behavior of a parabola using a coordinated set of lines, rays, perpendicular constructs, and intersection points, while also highlighting tangent relationships. The key math ideas include the definition of a parabola via locus (focal–directrix/constant-distance reasoning), locus construction, tangent geometry, and measuring angular relations at relevant points. Construction highlights: it uses Line, Point, and Segment to create the foundational geometric elements; Parabola to define the parabola itself; OrthogonalLine to enforce perpendicular constraints; Intersect to determine crucial intersection points; Ray and Angle to set and evaluate directed relations; and Tangent to construct the tangent line at the appropriate point on the parabola. The scene is organized around multiple named objects (including the parabola f), auxiliary points, and angle/annotation elements (e.g., α). Suitable for advanced high-school geometry and early university analytic/constructive geometry lessons, as well as student explorations focusing on parabola properties and dynamic geometric verification.

GeoGebra Commands & Parameters

  1. Line(L, M) → f
  2. Parabola(A, f) → c
  3. Point(c) → B
  4. Segment(A, B) → g
  5. OrthogonalLine(B, f) → h
  6. Intersect(f, h) → C
  7. Segment(C, B) → i
  8. OrthogonalLine(D, f) → j
  9. Intersect(c, j, 1) → E
  10. Ray(E, D) → k
  11. Line(E, A) → l
  12. Intersect(c, l, 2) → F
  13. Segment(E, F) → m
  14. OrthogonalLine(F, f) → n
  15. Point(n) → G
  16. Ray(F, G) → p
  17. Point(m) → H
  18. Angle(L, C, B) → α
  19. Intersect(c, k) → K,
  20. Tangent(K, c) → r,
  21. OrthogonalLine(K, r) → s
  22. Intersect(c, p) → N, O
  23. Tangent(N, c) → t,
  24. OrthogonalLine(N, t) → a
  25. Point(q) → P
  26. Ray(N, P) → b

AI Drawing Prompt Reference

Draw a reference line and use it together with a designated point A to define a parabola as the locus. Construct a point B on the parabola from an intersection between the parabola and a perpendicular line to the reference line through B’s construction. Connect A and B with a segment, then build the perpendicular through B to the reference line and intersect it with the reference line to obtain C. Mark the angle α formed by the reference line and the segments/rays through C and B. Next, place another point E by intersecting the parabola with a second perpendicular to the reference line through a constructed point. From E, draw a ray toward a direction set by another constructed point D, and draw the line through E and A to meet the parabola again at F. Drop a perpendicular from F to the reference line to define a point G, and draw a ray from F through G. Finally, at key intersection points with the constructed rays/perpendiculars, draw tangents to the parabola and use corresponding perpendicular feet to highlight the tangent–orthogonality relationships, keeping the marked angle α and tangent lines visible.
The prompt above was compiled from the original drawing commands and is for reference only.