My son is taking a calculus course in high school this year. While talking to him about his homework, I have come to realize that his knowledge of trigonometry is pretty weak. He said that they were supposed learn trigonometry last spring after the COVID-19 pandemic hit and school switched to fully online. Needless to say, the end of the school year didn’t go as planned.

So I decided to make a cheat sheet that contains all of the essential information on trigonometry that he will need for his calculus class—reference triangles, the unit circle, some trigonometric identities, and so forth. (I also knew that I could give it to my students the next time I taught Calculus.) I wanted it to be compact. I didn’t want to go overboard with the trig identities, for instance. I was trying to think about which ones we use again and again.

Here’s what I came up with—one sheet, front and back. Feel free to download this pdf for yourself or to share with your students. If I left anything off, let me know in the comments. (I will admit that I did not include anything about inverse trig functions. Maybe that’s for version 2.0.)