Beautiful problem about polyhedrons
106618
A Regular Tetrahedron is a cool Polyhedron.
16016
Coloring dodecahedron
90056
A synthetic geometrical proof required on a result regarding Isosceles triangles.
83449
Proof with 3D vectors
48339
A triangle with vertices on the sides of a square, with one at a midpoint, cannot be equilateral
15417
Tricky problem on skew-symmetric matrices
83872
Isomorphisms for graphs with loops and multiple edges
49879
A bipartite graph with a perfect matching has a vertex with each edge contained in a perfect matching
47443
Iterated polynomial problem
152478
Is there a homeomorphism between the $n$-dimensional cube to the $n$-dimensional simplex that doesn't create hard corners?
71711
Why a tesselation of the plane by a convex polygon of 7 or more sides is not possible?
157079
Maximal cardinality of a family of pairwise disjoint "figure eights" in the plane
130706
Group presentations and the Dihedral Group
68172
Erdős-Straus conjecture
132070
A challenge on the parabola
141101
Russia (2000) contest:Prove the existence of a pair of rows and columns with intersections differently coloured
11393
The center of the dihedral group