In a polygon, an exterior angle is formed by a side and an extension of an adjacent side. The sum of exterior angles in any convex polygon always adds up to 360 degrees, as shown in the 2 visual proofs below. Therefore, for all equiangular polygons, the measure of one exterior angle is equal to 360 divided by the number of sides in the polygon.
A triangle with sides π (3.14), e (2.71), and the Golden Ratio (1.61) is almost a right triangle!
Geometric composition involving equilateral triangles
The neat magic square featured on this stamp was created by Brazilian mathematician Inder Taneja. This square, called IXOHOXI magic square, not only shows common properties like other magic squares, as well as being pandiagonal, but also include extra properties such as symmetries, rotations and reflections.
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The regular hexagon hidden in a cube unfolds to a straight line on a net of the cube.
Indian mathematician Nārāyaṇa (1356) is the originator of the “Inscribed Lotus” (Padma Vrtta, a magic diagram constructed with the numbers of the 12×4 magic rectangle), in which every group of 12 numbers has the same sum 294.
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A strange right-triangle involving the unit imaginary number i
Repeated barycentric subdivision results in a gorgeous fractal-ish pattern.