Question 131623
Draw a circle. Draw a diameter of the circle. Now draw a line tangent to that diameter at one endpoint. So it hits the endpoint of the diameter, and that is the only point it hits on the circle. You should have a theorem telling you the angle between this line and the diameter. Draw a line similarly at the diameter's other endpoint. That angle is the same (look for the theorem telling you what the angle is, or make a good guess from your picture). Now go back to the beginning of the book. You learned some theorem about how 2 lines are related if they both are related to a third line in the same way (it's the special way those angles are going to tell you).  I did not want to give you the answer... hopefully this will make you think just enough.  I hope it clarified things a bit.  Sorry if it didn't... If that's the case, draw your picture, make a guess, and look for theorems to show why it looks that way.  Good luck!