Given a triangle, extend two sides in the direction opposite their common vertex. The circle tangent to these two lines and to the other side of the triangle is called an excircle, or sometimes an escribed circle. The center J_i of the excircle is called the excenter and lies on the external angle bisector of the opposite angle. Every triangle has three excircles, and the trilinear coordinates of the excenters are -1:1:1, 1:-1:1, and 1:1:-1. The radius r_i of the excircle i is called its exradius.