In der Geometrie eine von drei sich schneidenden Gerade begrenzte Figur. Man unterscheidet ungleichseitige D. mit unterschiedl. Seiten und Winkeln, gleichseitige D. mit gleichen Seiten und Winkeln, gleichschenklige mit je zwei gleichen Seiten und Winkeln, rechtwinklige D. mit einem 90-Winkel, spitzwinklige mit einem Winkel über 90. Die Winkelsumme ebener D. beträgt 180, D. auf Kugeloberflächen bezeichnet man als sphärische D.
ETYM Latin triangulum, from triangulus triangular; tri- (see Tri-) + angulus angle: cf. French triangle. Related to Angle a corner.
1. A percussion instrument consisting of a metal bar bent in the shape of an open triangle.
2. A three-sided polygon; SYN. trigon, trilateral.
3. Any of various triangular drafting instruments used to draw straight lines at specified angles.
In geometry, a three-sided plane figure, the sum of whose interior angles is 180ş. Triangles can be classified by the relative lengths of their sides. A scalene triangle has three sides of unequal length; an isosceles triangle has at least two equal sides; an equilateral triangle has three equal sides (and three equal angles of 60ş). Triangles can also be classified by their angle measures: a right triangle has one right (90ş) angle; an acute triangle has three acute (less than 90ş) angles; an obtuse triangle has one obtuse (greater than 90ş) angle; an equiangular triangle has three equal angles. (All equilateral triangles are equiangular, and vice versa.) If the length of one side of a triangle is l and the perpendicular distance from that side to the opposite corner is h (the height or altitude of the triangle), its area A = ˝ (lh).
(Astronomie) Triangulum, zwei kleine Sternbilder am nördl. u. südl. Himmel.