The unit circle can be used to project sin, cos and tan simultaneously in this animated diagram.
The graphs of sin and tan are projected horizontally (sin is the "wave") and cos is projected vertically.
Written using JavaScript and D3. Inspired by Tony Garnock-Jones' post where he generates the same animation using Squeak.
Requires a SVG-capable browser e.g. Mozilla Firefox or WebKit (Google Chrome, Safari &c.) — anything but Internet Explorer!