Online Geometry Problems, High School, College

Online Geometry Problem 475: Tangent Circles, Secant, Tangent, Parallel

The figure shows the circles C1 and C2 internally tangent at A. Line ABC is a secant, line L1 is tangent to C1 at C and line L2 is tangent to C2 at B. Prove that lines L1 and L2 are parallel.

Internally Tangent circles