Tangent lines in circles
Using the tools at the top of the screen
Measure angle H and angle B in circle 1
Measure segments DF and EF in circle 2
To measure angles...
Click the angle tool, then click on 3 points already on the screen.
To measure segments...
Click the distance tool, then click the two endpoints of the segment.
After you have measured segments and angles, use the move tool to drag points around.