As you may or may not know, I'm learning for Math teacher. So, yesterday evening the new "schoolyear" started with a class in Geometry. I've studied applied mathematics in 1991-1993, but never finished the study, in 1993 I switched to computer sciences but I've always been interested in math. However, if you're not working with it for a while, you really tend to forget quite a bit. So this geometry lesson was a good refresher.
The tangent of a circle is always perpendicular to the radius going through that point. A very nice geometry "drawing" application is Geogebra. It's free, runs on all platforms (java) and is localized in many languages. I created the image below with Geogebra to visualize the above thesis.
