In this lesson, Julie Harland shows how to derive the identity for the tangent of the sum and difference of angles or real numbers. She explains how to rewrite the tangent in terms of sine and cosine, and then uses those identities to derive the formula. She provides an example of applying the formula to find the tangent of a sum when given the tangents of two angles. She also explains how to apply the formula to find the tangent of a difference when given the tangents of two angles. Check out the full video on yourmathgal.com for more information.
This video derives the identity for the tangent of the sum and difference of angles (or real numbers), and provides an example using the identity if you know the tangents of two angles, but not their sum.
More free YouTube videos by Julie Harland are organized at http://yourmathgal.com