At 12 seconds into the video, cot(theta) is listed as cos(theta) / tan(theta), but it should say cot(theta) = cos(theta)/sin(theta).
In this trigonometry lesson, viewers learn how to prove or verify trigonometric identities. The instructor presents three different trigonometric identities to be verified and walks through the steps to solve each one. The lesson emphasizes the importance of knowing fundamental identities and Pythagorean identities, as well as the ability to manipulate one side using identities until it looks like the other side. Viewers are encouraged to put everything in terms of cosines and sines and to be creative in their approach to solving identities.
Shows steps for proving (or verifying) Trigonometric Identities;
More free YouTube videos by Julie Harland are organized at http://yourmathgal.com