6.3 Sum and Difference Identities

In this lesson, I will teach you the sum and difference identities. Before you start this section make sure you have mastered all the fundamental identities. For example, you should know how to verify a trigonometric identity using fundamental identities. Also, you should have a solid understanding of evaluating trigonometric functions especially with angles that don’t require a calculator. This lesson is a continuation of learning about trigonometric identities and how we can apply identities to solve various problems. My goal in this section is to get you to understand how learning more identities allows us to solve a wider range of problems. As always, it's critical that you do all the practice problems as trigonometric identities are a very important and widely used part of higher level mathematics.


  1. Watch the Lesson Video First - Take Good Notes.
  2. Next, Scroll All the Way Down the Page to View the Practice Problems - Try Them On Your Own.
  3. Check the Solutions to the Practice Problems by Looking at the Answer Key at the End of the Worksheet.
  4. However, YOU MUST Still Watch the Video Solutions to the Practice Problems; These Are the Videos Labeled EX A, EX B, etc. - They Are Located Next to the Lesson Video.
  5. After Doing All of the Practice Problems - Complete the Section and Advance to the Next Topic.

Practice Problems Worksheet:

6.3 Sum and Difference Identities Preview.pdf
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