I was recently informed of two small errors in my Trigonometric Identities "cheat sheet" given in my blog post titled "Trigonometry: Proving Trigonometric Identities," originally posted on March 6, 2012.
I have since corrected those errors. I have updated the original post with a notice to that effect. I also corrected the errors in the accompanying Google Document "cheat sheet" I shared on that post. If you downloaded this "cheat sheet" before 03/10/2015, please re-visit the link given in the original post and download the new version.
I am sorry for an inconvenience.