Points A,M1,M2 and C are on a line in this order. Let k1 the circle with center M1 passing through A and k2 the circle with center M2 passing through C. The two circles intersect at points E and F. A common tangent of k1 and k2, touches k1 at B and k2 at D. Show that the lines AB,CD and EF intersect at one point. geometrycommon tangentcirclesconcurrentconcurrency