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Fractal Tessellations from Proofs of the Pythagorean Theorem
L. Kerry Mitchell
Mathematics Department
University of Advancing Technology
2625 West Baseline Road
Tempe, AZ 85283 USA
Email: kmitchel@uat.edu
Abstract
The Pythagorean theorem can be proven geometrically through the use of dissections of squares and triangles. Four
of these decompositions are paired into two compound dissections, which are used to create novel images.
Pythagorean Theorem
Many proofs of the Pythagorean theorem are given in the literature, for example, at the MathWorld web
site [1]. Of particular interest to this work are dissection proofs, wherein a figure is cut into pieces and
reassembled into another figure with equal area. Several of these are collected at the Cut The Knot web
site [2].
Figure 1: Dissection Proofs
In this work, four dissections were used, as shown in Figure 1. Two were based on decomposing a
square into a smaller square and four congruent right triangles. The other two decomposed a right
triangle into a square and smaller similar right triangles. In each case, algebraically equating the area of
the larger figure with the sum of the areas of the smaller shapes leads to the Pythagorean theorem.
Fractal Tessellations
When dissection results in pieces that can be further dissected, a fractal tessellation can be created by
infinitely continuing the process. In this case, each dissection produced both squares and right triangles,
which could be further broken down. Each square decomposition was paired with a triangle dissection
into a compound process; they are shown in Figure 2. The first two panels show the first square and first
triangular dissections paired. The rotation of the inside square is a free parameter, and the two cases
correspond to 20 and 45 degrees, respectively. As the rotation increases, the size of the outer smaller
squares increases, to a maximum at 45 degrees. The last two panels show the second square and second
triangular dissections paired. The rotation angles are 20 degrees and approximately 32 degrees. In the
last panel, the rotation was chosen such that the central and outer small squares are congruent.
20 degrees 45 degrees 20 degrees ~31.7 degrees
Compound Dissection 1 Compound Dissection 2
Figure 2: Compound Dissections
New Designs
These compound dissections were used to create new artworks, some of which are shown in Figure 3.
All were generated using the program Ultra Fractal [3]. . These images merely hint at some of the
possibilities open to the algorithmic artist. Of course, there are other ways to decompose squares and
triangles into more squares and triangles, and each of those can be incorporated into a fractal tessellation.
The varieties offered, combined with the freedom afforded by rotating the central square, make this
technique quite a fruitful one.
Compound 1 Compound 1 Compound 2 Compound 2
20 degrees rotation 45 degrees 20 different rotations ~31.7 degrees
20 iterations 7 iterations 4 iterations 7 iterations
References
[1] E. W. Weisstein. “Pythagorean Theorem,” http://mathworld.wolfram.com/PythagoreanTheorem.html,
1999.
[2] A. Bogomolny, “Pythagorean Theorem,” http://www.cut-the-knot.org/pythagoras/index.shtml, 1996.
[3] Slijkerman, F., “Ultra Fractal,” http://www.ultrafractal.com, 1997.

 

 

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