Hi, I'm a grade 12 high school student in Canada. This semester I'm taking math, chemistry, and physics and I've been really enjoying these classes so far. However, one question I can't even dare to ask my teachers is that why we are expected to memorize all those formula/equations. (ex/ Trig. Identities, Centripetal acceleration.) My math class is on Trig. and today my teacher gave us a sheet of paper which was full of equations (A Summary of Basic Identities and Formulae) and told us to memorize half of the stuff. So at home I started doing the h/w. I wrote down the identities repeatedly on a sheet of paper. However, I wanted to know how/why those identities work. So I went on Google and did a quick search. This http://oakroadsystems.com/twt/pythag.htm#squaredTop" [Broken] came up and 5 minute of reading it saved me from 30 minute + of repetitive memorization. So I was wondering why the teachers wouldn't show us how those stuff(ie trig. identities) were derived at the first place. Surely deriving trig. identities weren't hard at all. Maybe they are just too lazy -_-??