Construct the two possible tangent lines through a point, with compass and straightedge
(For assistance see www.mathopenref.com/consttangents.html)
1. Construct the two tangents to the circle that pass through the point P
2. CHALLENGE problem:
  (a) With a ruler, measure the radius of the circle and the length of a tangent line segment. (Easiest if you measure in millimeters.) From these, calculate the distance of P from the circle center.
  (b) Confirm your calculation by measuring the distance with a ruler.