What is Isosceles triangle?
[[Image:Triangle-isosceles.svg|120px|right|Isosceles triangle]] In [[geometry]], an '''isosceles triangle''' is a [[triangle]] that has two sides of equal length. Sometimes it is specified as having two ''and only 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 (mathematics)|golden triangle]], and the faces of [[bipyramid]]s and certain [[Catalan solid]]s. 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 [[pediment]]s and [[gable]]s of buildings. The two equal sides are called the legs and the third side is called the base of the triangle. The other dimensions of the triangle, such as its height, area, and perimeter, can be calculated by simple formulas from the lengths of the legs and base. Every isosceles triangle has an axis of symmetry along the [[perpendicular bisector]] of its base. The two angles opposite the legs are equal and are always [[acute angle|acute]], so the classification of the triangle as acute, right, or obtuse depends only on the angle between its two legs. {{Polygons}} {{math-stub}} [[Category:Polygons]]