The excenter of an ex-tangential quadrilateral lies at the intersection of six angle bisectors. In a tangential quadrilateral, the four angle bisectors meet at the center of the incircle. The perpendicular bisectors of any two sides of a triangle intersect in exactly one point. Construct the perpendicular bisectors to the two segments AA and BB. The internal and external bisectors of an angle are perpendicular. Medians and angle bisectors are special cases of cevians. The perpendicular bisectors of the sides also play a prominent role in triangle geometry. Hence, the center is the point of intersection of any two perpendicular bisectors. Three other area bisectors are parallel to the triangle's sides. The cleavers are parallel to the angle bisectors. The intersections of these angle bisectors give the centers of solution circles. For all these systems both photon world lines represent the angle bisectors of the axes. The incenter is the point where the internal angle bisectors of formula 3 meet. The intersection P of these two bisectors is the pole of the planar displacement. Points are arranged to pairs what defines n/2 lines as their bisectors.