### Triangle

**TRI'ANGLE**, *noun* [Latin triangulum; tres, tria, three, and angulus, a corner.] In geometry, a figure bounded by three lines, and containing three angles. The three angles of a *triangle* are equal to two right angles, or the number of degrees in a semicircle.

If the three lines or sides of a *triangle* are all right, it is a plane or rectilinear *triangle*

If all the three sides are equal, it is an equilateral *triangle*

If two of the sides only are equal, it is an isosceles or equicrural *triangle*

If all the three sides are unequal, it is a scalene or scalenous *triangle*

If one of the angles is a right angle, the *triangle* is rectangular.

If one of the angles is obtuse, the *triangle* is called obtusangular or amblygonous.

If all the angles are acute, the *triangle* is acutangular or oxygonous.

If the three lines of a *triangle* are all curves, the *triangle* is said to be curvilinear.

If some of the sides are right and others curve, the *triangle* is said to be mixtilinear.

If the sides are all arcs of great circles of the sphere, the *triangle* is said to be spherical.