Precalculus

Lesson 3: Trigonometric Functions Topic 3: Reference Angles Examples : Find the reference angle for each angle. 1. Find the reference angle for 218?. Find the positive acute angle made by the terminal side of the angle and the x-axis: The reference angle for 218? is 218? - 180? = 38? 2. Find the reference angle for 1387 ? First find a coterminal angle between 0? and 360?. Divide 1387 by 360 to get a quotient of about 3.9. So subtract 360 three times. 1387? ? 3(360? ) = 307?. The reference angle for 307 ? is 360? ? 307? = 53? 360? ? 307? = 53? 3. Find the reference angle for -237? Find a coterminal positive angle by adding 360?: -237? + 360? = 123? The reference angle for 123? is 180? - 123? = 57?. 180 ? ? 123 ? = 57 ? 180? ? 123? = 57? Practice