College Algebra & Trigonometry, 2018a

388 CHAPTER 9. GRAPHING THE TRIGONOMETRIC FUNCTIONS
2. An angle of 241 ◦ terminates in Quadrant III. To find the reference angle, we
would subtract 180 ◦ from the angle: 241 ◦ − 180 ◦ =61 ◦ .
241 ◦ 61 ◦
3. An angle of 327 ◦ terminates in Quadrant IV. To find the reference angle, we
subtract the angle from 360 ◦ : 360 ◦ − 327 ◦ =33 ◦ .
327 ◦ 33 ◦
Once we know the reference angle, we can find the trigonometric functions for
the original angle itself. In example 1, we had 128 ◦ , an angle in Quadrant II with
a reference angle of 52 ◦ . Therefore, if we want to find the sine, cosine and tangent
of 128 ◦ , then we should find the sine, cosine and tangent of 52 ◦ and apply the
appropriate positive or negative sign.