Brocard points

In geometry, Brocard points are special points within a triangle. They are named after Henri Brocard (1845–1922), a French mathematician. In a triangle ABC with sides a, b, and c, where the vertices are labeled A, B and C in counterclockwise order, there is exactly one point P such that the line segments AP, BP, and CP form the same angle, ω, with the respective sides c, a, and b, namely that Point P is called the first Brocard point of the triangle ABC, and the angle ω is called the Brocard angle of the triangle. This angle has the property that where are the vertex angles respectively. There is also a second Brocard point, Q, in triangle ABC such that line segments AQ, BQ, and CQ form equal angles with sides b, c, and a respectively. In other words, the equations apply. Remarkably, this second Brocard point has the same Brocard angle as the first Brocard point. In other words, angle is the same as The two Brocard points are closely related to one another; In fact, the difference between the first and the second depends on the order in which the angles of triangle ABC are taken. So for example, the first Brocard point of triangle ABC is the same as the second Brocard point of triangle ACB. The two Brocard points of a triangle ABC are isogonal conjugates of each other. The most elegant construction of the Brocard points goes as follows. In the following example the first Brocard point is presented, but the construction for the second Brocard point is very similar. As in the diagram above, form a circle through points A and B, tangent to edge BC of the triangle (the center of this circle is at the point where the perpendicular bisector of AB meets the line through point B that is perpendicular to BC). Symmetrically, form a circle through points B and C, tangent to edge AC, and a circle through points A and C, tangent to edge AB. These three circles have a common point, the first Brocard point of triangle ABC. See also Tangent lines to circles. The three circles just constructed are also designated as epicycles of triangle ABC.