Merry Christmas! In the previous post I introduced the idea of an irreducible representation and showed that except in fields of low characteristic, these representations decompose completely. In this post I'll present Schur's Lemma at talk about what Schur and Maschke tell us about homomorphisms of representations. 1. Motivation Fix a group $latex {G}&fg=000000$ now,… Continue reading Representation Theory, Part 2: Schur’s Lemma
Category: Mathematics
Representation Theory, Part 1: Irreducibles and Maschke’s Theorem
Good luck to everyone taking the December TST tomorrow! The goal of this post is to give the reader a taste of representation theory, a la Math 55a. In theory, this post should be accessible to anyone with a knowledge of group actions and abstract vector spaces. Fix a ground field $latex {k}&fg=000000$ (for all… Continue reading Representation Theory, Part 1: Irreducibles and Maschke’s Theorem
Three Properties of Isogonal Conjugates
In this post I'll cover three properties of isogonal conjugates which were only recently made known to me. These properties are generalization of some well-known lemmas, such as the incenter/excenter lemma and the nine-point circle. 1. Definitions Let $latex {ABC}&fg=000000$ be a triangle with incenter $latex {I}&fg=000000$, and let $latex {P}&fg=000000$ be any point in… Continue reading Three Properties of Isogonal Conjugates
Set Theory, Part 2: Constructing the Ordinals
This is a continuation of my earlier set theory post. In this post, I'll describe the next three axioms of ZF and construct the ordinal numbers. 1. The Previous Axioms As review, here are the natural descriptions of the five axioms we covered in the previous post. Axiom 1 (Extensionality) Two sets are equal if… Continue reading Set Theory, Part 2: Constructing the Ordinals
Set Theory, Part 1: An Intro to ZFC
Back in high school, I sometimes wondered what all the big deal about ZFC and the Axiom of Choice was, but I never really understood what I read in the corresponding Wikipedia page. In this post, I'll try to explain what axiomatic set theory is trying to do in a way accessible to those with… Continue reading Set Theory, Part 1: An Intro to ZFC
Why do roots come in conjugate pairs?
This is an expanded version of an answer I gave to a question that came up while I was assisting the 2014-2015 WOOT class. It struck me as an unusually good way to motivate higher math using stuff that people notice in high school but for some reason decide to not think about. In high… Continue reading Why do roots come in conjugate pairs?
What leads to success at math contests?
Updated version of generic advice post: Platitudes v3. I think this is an important question to answer, not the least of reasons being that understanding how to learn is extremely useful both for teaching and learning. [1] About a year ago [2], I posted my thoughts on what the most important things were in math… Continue reading What leads to success at math contests?
Writing Olympiad Geometry
I always wondered whether I could generate olympiad geometry problems by simply drawing lines and circles at random until three lines looked concurrent, four points looked concyclic, et cetera. From extensive experience you certainly get the feeling that this ought to be the case -- there are tons and tons of problems out there but… Continue reading Writing Olympiad Geometry
A Sampler of Harvard Math
I was in Boston over this weekend for the 2014 Harvard-MIT Math Tournament. Before the contest on Friday, I sat in a few of the undergraduate math classes. They were pretty nice; I was actually able to learn some higher math that just by sitting in, despite the fact that I didn't have the necessary… Continue reading A Sampler of Harvard Math
Constructing Parallelograms
This is a reflection of a talk I gave today. Hopefully these reflections (a) help me give better talks, and (b) help out some others. Today I was worked from 6PM-8PM with the Intermediate group at the Berkeley Math Circle, middle school students maybe one or two standard deviations above the average honors student. My… Continue reading Constructing Parallelograms
Power Overwhelming 