 Matt, trigonometry is clearly the most boring, irrelevant and ancient part of all maths. It's the thing that everybody is forced to learn at school. I can't remember liking trigonometry. Why on earth have you decided to write a book about it? You sound just like my publishers. And so tell me more. Come on. I was like, no, that's the point. I think it would be very funny to write a book about trigonometry, the famously boring and annoying subject. But my theory is...