Pentagrams, Pentagons, Doodles and Trigonometry

I don’t normally do this, but I couldn’t decide whether this post belonged on my other blog or this one. The other is for notes, and this post is pretty notey, so I put it there. But it’s mathsy too, so some people here might like it: http://insimpleterms.blog/pentagons-pentagrams-doodles-and-trigonometry