This is a wonderful puzzle I found in the puzzle collection of The Guardian newspaper, the original source being Martin Gardner. The beauty of this puzzle is that one needs to use simple rules of geometry and we do not need any trigonometry at all.
Please have a look at the figure above. Prove that angle C in the illustration equals the sum of angles A and B.
Please send your answers either directly on the blog site as comments, or to me at firstname.lastname@example.org. If you like the puzzle, please share it with others. If you have interesting puzzles to share, please send them to me at my e-mail given above.