In The Feynman Lectures on Physics, Volume 3 Chapter 5, Feynman poses a challenge to the reader: show that a particular combination of plus, minus and zero states of a spin one particle transforms under a rotation just like a vector does. In this previous video I reviewed the details of proving it for rotations around the z-axis. Here I go over the more complicated proof for rotations around the y-axis.
Category: Trigonometry
In The Feynman Lectures on Physics, Volume 3 Chapter 5, Feynman poses a challenge to the reader: show that a particular combination of plus, minus and zero states of a spin one particle transforms under a rotation just like a vector does. Here I go over how to work that problem using only what was covered in the book up to that point.
A moderately difficult trig identity: prove 
A step-by-step example of how to find the area of a polygon
Finding the area of a polygon seems impossible given just the side length or just the length of a radius or apothegm. But here’s how to do it, step by step.
Here’s one of the things about complex numbers which is easier if you know it so well you don’t have to think about it: the formula for sin x. Nice and easy. Assumes you already know Euler’s formula, eix = cos x + i sin x.
Assuming you know the basics (tan=sin/cos, etc), here are strategies and examples for proving simple trig identities.