Natasha....this is just like this one:
http://web2.0calc.com/questions/determine-whether-a-tangent-line-to-circle-o-is-shown-in-the-diagram-for-ab-7-75-ob-4-and-ao-8-75-explain-your-reasoning-the-f#r2
Look and see what jboy314 and I did......I think you can handle it .....