Originally Posted by

**topsquark** (Since this was a new question, it probably should go in a new thread.)

I can't do the sketch as my computer died last week and given the trouble I was having with my scanner's software anyway, I've decided not to try to ressurect it.

However, if you sketch the situation you should be able to verify what I'm saying.

Sketch a line PT tangent to a circle. Now draw a radius out to point T. These two lines ALWAYS meet at a right angle.

Now sketch the line PM. Since M is the closest point on the circle to P if we extend this line it will pass through the origin.

What this means is that OPT is a right triangle, with legs of length r and 19.8, and a hypotenuse of length (r + 13.2).

Thus

r^2 + 19.8^2 = (r + 13.2)^2

Now you can solve for r.

-Dan