It's a long time since I needed to do any trigonometry, but the other night we were ordering some bookshelves off the internet and I had to use my old skills. The idea was to get some along each wall by a corner and then another one in the corner at 45 degrees. I had to use a picture and some maths to determine whether the whole arrangement would fit in the room or not.
Or at least it would on paper. The proof will be in the putting (up).