This topic is quite a small one and so is best demonstrated by answering the typical exam question on this topic (it is quite similar to tangent of a circle questions).
Question
Answer
The answer is below this so if you are reasonably confident try and answer the questions yourself first and then compare your answer. If you are new to this topic or completely lost then the answer below walks you through the solution in a lot of detail and there is then a link to some more questions at the bottom of the page for you to try using this solution as a guide.
Nerd Herd Corner 