 Like things like Pythagoras and your trig ratios, they're the most advanced maths that most people were forced to learn at school. So they've become this kind of mascot for difficult, boring, pointless mathematics. And so I took that on as a challenge to write a book and explain, no, I know when you were forced to learn it as a teenager, it wasn't very exciting, but without trigonometry, our modern world just wouldn't be possible.