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Course: Trigonometry
Topic: Trigonometric Identities
Subtopic: Sum/Difference Identities

Overview

Our current arsenal of identities include the reciprocal, ratio, and Pythagorean. In today's lesson we add to that the sum and difference identities which expand trig functions of a sum of angles or of a difference of angles such as cos(x+π/3). These will be useful, among other things, to evaluate trig functions of non-"nice" angles (such as 15° or π/12 as opposed to the "nice" angles such as 45° or π/2).

Objectives

By the end of this topic you should know and be prepared to be tested on:

Terminology

Define: sum of angles, difference of angles