Wikipedia:Today's featured article/May 14, 2004

A triangle is one of the basic shapes of geometry: a two-dimensional figure with three vertices and three sides which are straight line segments. Elementary facts about triangles were presented by Euclid in books 1-4 of his Elements in around 300BC. In Euclidean geometry, the sum of the angles α + β + γ is equal to two right angles (180° or π radians). This allows determination of the third angle of any triangle as soon as two angles are known. (more...)

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