## Proof without Words: Angle Sum and Difference Formulas

One of my favorite images:

Posted 4 March, 2013 by in Classroom, Trigonography

## The Geometry of the Power Series for Trig Functions

When you (like I) think that the trig functions are best understood as segments within the Complete Triangle, you tend to believe that just about every important fact about those functions has a nifty geometric interpretation. (See other posts in this category.) Why shouldn’t we expect this to be true of the functions’ power series? […]

Posted 17 July, 2012 by in Open Question, Trigonography

## Proof with Too Many Words: Derivatives of Sine and Cosine

I’d like to think that the following constitutes a Proof without Words of the formulas for the derivatives of sine and cosine. Unfortunately, it seems that words may be in order, so I wrote some here: “Calculus-free Derivatives of Sine and Cosine” … even though, strictly speaking, the proof isn’t entirely calculus-free. (Why we expect the […]

Posted 17 July, 2012 by in Trigonography

## Proof without Words: The Law of Cosines

(I really need to put this onto a poster.)

Posted 17 July, 2012 by in Trigonography

## (Almost) Everything you need to remember about Trig …

The “Complete Triangle” figure —which represents the six trig functions as lengths of segments— is something of an obsession of mine, and has been for some time. It’s the basis of my triple-ricochet company logo and name of my iOS-specific brand, tricochet, and it’s the subject of my very first iOS app (one of the […]

Posted 17 July, 2012 by in Trigonography