14 Answers votes newest views recent 12Examples of mathematics motivated by technological considerations 12real symmetric matrix has real eigenvalues - elementary proof 9The “Dzhanibekov effect” - an exercise in mechanics or fiction? Explain mathematically a video from a space station 8Is every finite group a group of “symmetries”? 7Why are so few operations with arity bigger than 2? 6Why is a topology made up of ‘open’ sets? 6Does every ellipse inside a tetrahedron inside a ball fit in a triangle inside the ball? 2Relating the angle between two vectors to max and min eigenvalues 2Why worry about the axiom of choice? 2Which norms have rich isometry groups? 1Optic fibers after Joseph O’Rourke 1Towards a metric characterization of Euclidean spaces 1Find symmetries of a tree 0Intuition for mean curvature.