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Problem Solution included

A set that shifts into its complement

Can arbitrarily small translations turn a subset of the real line into its complement?

real analysislinear algebraset theory
Exploration

From planar graphs to the five Platonic solids

Count vertices, edges, and faces; add a point at infinity; then discover why there are exactly five regular convex polyhedra.

geometrygraph theorytopology
Problem Solution included

Cutting a cube

How many straight cuts does it take to separate a cube into 27 unit cubes, even if you can rearrange the pieces?

geometrypuzzles
Exploration

Four equal regions: two bisections and a turn

Two easy bisections leave one imbalance. A quarter-turn suggests how to remove it—but we must account for the jumps in a point count.

geometrycountingpuzzles

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