This lesson teaches how to derive the formula for the cosine of the sum of two angles using the unit circle definition of sine and cosine, the Pythagorean identity, and the distance formula. The video also highlights the importance of knowing that the cosine of a plus b is not equal to the cosine of a plus the cosine of b. By the end of the lesson, students will have learned how to derive the formula for the cosine of the sum of two angles and apply it to compute angles like the cosine of 60 degrees plus 45 degrees.
This video shows the formula for deriving the cosine of a sum of two angles.
More free YouTube videos by Julie Harland are organized at http://yourmathgal.com