triangle A three-sided polygon. The sum of the interior angles of a triangle is always 180°, unless the triangle is drawn in a non-Euclidean geometry. Triangles can be classified either by their angles, as acute, obtuse, or right; or by their sides, as scalene (all different), isosceles (two the same), or equilateral (all equal). Related category MATHEMATICS Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) |