A line MN is given in the plane. Consider circles k1, k2 tangent to the line at points M, N, respectively, while touching each other externally. Let X be the midpoint of the segment PQ, where P, Q are in this order tangent points of the second common external tangent of the circles k1, k2. Find the locus of the points X for all pairs of circles of the specified properties. geometryLocustangent circlescommon tangent