Baravelle's Spiral: Infinite Series in Geometry

Baravelle's Spiral: Infinite Series in Geometry
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2020-04-27 10:03
This GeoGebra example demonstrates a spiral-like shrinking pattern formed by repeatedly constructing similar polygons and mirroring them, visually representing the summation of a geometric series. The core mathematical concepts involve infinite series, limits, and geometric distribution—each successive polygon's area decreases by a fixed ratio, and the total area converges to a finite value. Construction highlights: using GeoGebra commands Polygon to create the initial polygon poly1, Sequence to generate a chain of nested polygons, and Mirror to flip each new polygon, producing the spiral effect. Key objects include poly1, poly2, poly3, auxiliary points a-j, variable n, color labels lred, lblue, lblack, and text2. This is suitable for high school and above, for learning sequence limits and geometric series, or as a mathematical exploration activity; it also serves as an intuitive visual aid for introductory calculus, linking abstract infinite series to concrete geometric shapes.

GeoGebra Commands & Parameters

  1. Polygon((1.4142135623730951; 225°), (1.4142100000044873; 314.9998556728185°), (1.4142064376269061; 45°), (1.4142100000044873; 135.00014432718154°)) → poly1, a, b, c, d
  2. Polygon((-1, 1), (-1, 0), (5.551115123125783E-17, 1)) → poly2, e, f, g
  3. Polygon((1, -1), (1, 0), (0, -1)) → poly3, h, i, j
  4. Sequence(Dilate[Rotate[poly2, (((-k) * 45))°], 0.70711^(k)], k, 1, n - 1) → lred
  5. Mirror(lred, (0, 0)) → lblue
  6. Sequence(Dilate[Rotate[poly1, (((-k) * 45))°], 0.70711^(k)], k, 1, n) → lblack

AI Drawing Prompt Reference

Draw a spiral pattern formed by nested rotated polygons. Start with a tilted square, then add two right triangles, one at the upper left and one at the lower right. Rotate each triangle counterclockwise by 45 degrees repeatedly, scaling down by a factor of about 0.707 each time, to create two spiral chains. Also rotate and scale the original square in the same manner to form a third spiral chain. All shapes are centered at the origin, symmetrically arranged, shrinking inward to illustrate a geometric series with decreasing areas. Use distinct colors for different chains.
The prompt above was compiled from the original drawing commands and is for reference only.