### Speaking Of Wikipedia

The entry at Reflection is short and sweet. Unfortunately, there’s no version of our $\null [(x,y)\mapsto (a, b)]$ notation (the formulas are given in “vector” language). But that’s okay.

A little curiousity and some link-following brings us to the fabulous Euclidean Plane Isometry (“reflection” is one type of isometry [measure-preserving transformation … iso- as in isolate (“the same”) and metr as in, well, meter obviously … as opposed to a measure changing transformation like the “vertical stretch” $\null \sigma^3_y = [(x,y)\mapsto (x, 3y)]$). $wha$ ]). Even just by looking at the pictures, one could find out a lot of pretty interesting stuff here. And there’s plenty of perfectly intelligible expostion even if one were to skip almost all the equations (but you know I’m having none of that …). Wikipedia is just bottomless … you could just go on and on …

But there may not be much there that closely resembles a standard course in Precalculus. So look a little harder: this (PDF) Algebra Test is a pretty good first approximation of a 148 Midterm, so one could probably learn quite a bit from the entire bloody Online Course I found it in (by Robert Heal at Utah State U.; the first nonadvercrap link in this Google search). That’s as far as I’m likely to be willing to go for now … I’ve got a lot of reading to do …