Counting, Tessellations, and Hypercubes
Session Overview
The class opened with meditation and visual counting through sequences, number bases, and the new Count Tetris tool. It then explored convex polyhedra through nets, duals, and three-dimensional tessellations before moving into projections of tesseracts and higher-dimensional cubes. Throughout, the emphasis was on experiencing mathematical patterns directly and learning to ask productive questions.
Seeing numbers through structure
Numbers were represented in multiple geometric and sequential forms rather than only as symbols.
- Number forms: Examples included factor arrays, triangular and tetrahedral numbers, perfect squares, cubes, harmonics, factorials, and powers of two and three.
- Fibonacci sequence: Each term was built visibly from the previous two: 0, 1, 1, 2, 3, 5, 8, 13, and onward.
- Counting in other bases: Binary counting and skip-counting in bases such as 3, 5, 6, and 9 revealed patterns that are hidden when working only in base ten.
Practice with the visual counting tools
Use the course website’s counting tools on a phone or tablet and treat exploration as a regular practice.
- Count Tetris: Skip-count by different amounts, then change the base and observe how the spatial pattern changes.
- Suggested base exercise: Count by twos in base three, and repeat binary counting from zero through 15 or 16.
- Sequence fluency: Practice powers of two through 4096 and factorial counting through 7!.
Tessellations depend on the surrounding space
The polyhedra explorer showed nets, dual constructions, dihedral angles, and solids that fill three-dimensional space without gaps.
- Three-dimensional tessellation: The cube, truncated octahedron, and rhombic dodecahedron were used to illustrate space-filling structures analogous to a two-dimensional honeycomb.
- Flat versus curved space: Pentagons do not tessellate the Euclidean plane, but appropriately sized pentagons can cover spherical space. Hyperbolic space permits patterns, such as seven-sided cells, that do not fit in the flat plane.
- Duals and symmetry: A dual is formed from face-center relationships with vertex positions adjusted so the resulting solid has the required symmetry.
Projecting and constructing a tesseract
A cube’s changing two-dimensional shadow provided the analogy for viewing a fixed four-dimensional object through a changing three-dimensional projection.
- Dimensional construction: Extrusion follows point → line → square → cube → hypercube.
- Tesseract structure: A tesseract is a four-dimensional cube with 16 vertices, 32 edges, and eight cubic cells.
- Coordinates: Its vertices can be described with XYZW coordinates; each coordinate takes a positive or negative value, producing 2⁴ = 16 vertices.
- Rotations: Four-dimensional rotations occur in coordinate planes. There are 6 such rotations in four dimensions, 10 in five dimensions, and 15 in six dimensions—the triangular-number pattern.
- Higher dimensions: Repeated projection loses information but allows higher-dimensional cubes to be displayed through three-dimensional forms and ultimately on a two-dimensional screen.
Possible programming extension
A valuable extension would be to write a program that generates hypercube vertices, connects the correct pairs, and projects the result into lower dimensions. Deriving the projection equations and the counts of vertices, edges, and faces would connect the visual model to computation.
Learning to think mathematically
Understanding was treated as a continuum rather than an all-or-nothing state. The class emphasized staying with the mathematics itself, noticing patterns within its domain, and learning from strong questions—not only collecting answers.