Incircle and excircles of a triangle polygon with any number of sides that has an inscribed circle—one that is tangent to each side—is called a tangential polygon. Incircle and excircles of a triangle In geometry, the incircle or inscribed circle of a triangle is the largest circle contained in the triangle; it touches (is tangent to) the three sides. The center of the incircle is a triangle center called the triangle's incenter. An excircle or escribed circle of the triangle is a circle lying outside the triangle, tangent to one of its sides and tangent to the extensions of the other two. Every triangle has three
Line (geometry) ray, the "AD" ray is called the "opposite ray". Thus, we would say that two different points, "A" and "B", define a line and a decomposition of this line into the disjoint union of an open segment and two rays, "BC" and "AD" (the point "D" is not drawn in the diagram, but is to the left of "A" on the line "AB"). These are not opposite rays since they have different initial points. In Euclidean geometry two rays with a common endpoint form an angle. The definition of a ray depends upon the notion of betweenness for points on