In a circle C with centre O and radius r, let C1, C2 be two circles with centres O1, O2 and radii r1, r2 respectively, so that each circle Ci is internally tangent to C at Ai and so that C1, C2 are externally tangent to each other at A.
Prove that the three lines OA, O1A2, and O2A1 are concurrent. trigonometrygeometrygeometry unsolved