an isosceles triangle has two sides of equal length
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Isosceles triangle [SEP] Introduction
In geometry, an isosceles triangle is a triangle that has two sides of equal length. Sometimes it is specified as having "exactly" two sides of equal length, and sometimes as having "at least" two sides of equal length, the latter version thus including the equilateral triangle as a special case. Examples of isosceles triangles include the isosceles right triangle, the golden triangle, and the faces of bipyramids and certain Catalan solids. The mathematical study of isosceles triangles dates back to ancient Egyptian mathematics and Babylonian mathematics. Isosceles triangles have been used as decoration from even earlier times, and appear frequently in architecture and design, for instance in the pediments and gables of buildings.