Let gamma be a circle with center O and P a point outside gamma.

Construct a tangent line to gamma through point P using a straightedge only.

Prove the construction.

(In reply to re: Seriously by Charlie)

Indeed.

If we were to consider X to at an infinite distance from O (ie, / DPB approaches 0º) the / POX approaches 90º as the limit such that
/ YOP is almost a rightangle. 

Yes, as / DPB widens the points X, D, E and Y converge at a point to the left (on my sketch) of this vertical location.

I tried this in ACAD using a few different angle sizes for / DPB.  Back to a straightedge and pair of compasses.

Edited on March 15, 2008, 7:24 pm

Posted by brianjn on 2008-03-15 19:21:18