Le trapèze, problème de géométrie | Tangente

Arbelos: Archimedes' figure of semicircles | Tangente

Sam Loyd puzzle: 5 pieces, square or cross | Tangente

Elegant problem-solving methods (2) | Tangente

The beauty of mathematical problems often lies in an imaginative method—a "haha," as Martin Gardner called it—that makes the solution seem obvious, provided we can find a fresh perspective.

Quadrilateral types and names | Tangente

For the familiar convex quadrilaterals, the classification criteria are, first, whether the sides are parallel, then whether their lengths are equal, and finally whether there are any right angles.