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Course: Trigonometry
Topic: Circular Functions
Subtopic: Radian Measure

Overview

To date we have only measured angles in degrees, but today we will introduce a new angle measure called radian measure. It is based on irrational number pi (π) rather than the number 360. Notation caution: Radians don't (usually) have a symbol indicating radian measure, so leaving the degree mark off looks like radians! For example, tan(45) means the tangent of 45 radians. To indicate the tangent of 45 degrees you must write tan(45°). tan(45)≠tan(45°) ... check this electronically noting that the tan(45) must be evaluated in radian mode and tan(45°) must be evaluated in degree mode so set your device/software accordingly.

Objectives

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

• 3.2.1 Convert degrees radians (algebraically and electronically)
• 3.2.2 Common angles in radians (memorize π/6=30°, π/4=45°, etc.)
• 3.2.3 Evaluate trigonometric functions having inputs that are angles in radian measure (algebraically and electronically)

Terminology

Define: pi (π), radian, unitless measure

Supplementary Resources (recommended)

Everyone should READ THIS ARTICLE: Why Use Radian Measure?

You must be able to use a calculator (handheld or software) to work with angles in radians. If you have a handheld graphing calculator then these sites may help you learn about working in radian mode:

Supplemental Resources (optional)