"sinh" in Snell's Law? 1. The problem statement, all variables and given/known data I'm trying to understand some equations in my AS level textbook about Snell's Law 2. Relevant equations The equations are in the image below 3. The attempt at a solution I tried reading up about sinh but I don't fully understand what it is. Also I'm not sure what the term beside sinh is. It can't be a "1" and to seems like a small letter L which comes out of nowhere?