Trigonometry - an interactive right triangle

Having a limited understanding of trigonometry and wanting to learn a little more, I decided to see if I could create my own program containing an interactive "right triangle".

The attached program displays a simple grid in which - when the user click inside it - a right triangle with the hypotenuse at a specific angle is generated. Where exactly the user clicks determines where the triangle's hypotenuse and opposite sides meet. This in turn determines the hypotenuse's angle. The program then uses the difference in length of the triangle's sides to calculate the sine, cosine, and tangent (not through the System.Math functions, although they are used in a few places.)