<p>@brain…,</p>
<p>The problem you present is trivial. You just need two independent associations from the given data. Use similar triangles and the tangent-secant theorem. The latter is quadratic. Solve the system and you have your answer … as for showing the triangles are similar, you know the arcs are equal, and that CD is tangent, so a perp MUST bisect AB hence AB and CD are parallel … check a text for any theorems you want to cite (there are many you could use)</p>