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:
- 5.2.1 Use sum/difference formulae to evaluate trig functions
- 5.2.2 Use sum/difference formulae to prove other trig identities
- 5.2.3 Solve problems involving a sum or difference in the angle
Terminology
Define: sum of angles, difference of angles