Consider an acute triangle ABC and its altitudes from A ,B that intersect the respective sides at D,E. Let us call the point of intersection of the altitudes H. Construct the circle with center H and radius HE. From C draw a tangent line to the circle at point P. With center B and radius BE draw another circle and from C another tangent line is drawn to this circle in the point Q. Prove that the points D,P, and Q are collinear. geometrycollinearorthocenter