2.2 Finding Trigonometric Functions of Non-Acute Angles

This lesson is going to cover how to find the trigonometric functions of angles that are more than 90 degrees and less than 0 degrees. Let’s proceed.

1. The reference angle is always found with reference to the x-axis.
2. If the angle is greater than 90 degrees, solve using reference angles.
   • 1. Make sure 0 < theta < 360. If not, find coterminal angle.
   • 2. Figure out which quadrant the angle is in and find a reference angle.
   • 3. Draw a triangle and find 6 trig functions.

Finding the Reference Angle

1. In Quadrant 1: reference angle = angle in quadrant 1
2. In Quadrant 2: reference angle = 180 – angle in quadrant 2
3. In Quadrant 3: reference angle = angle in quadrant 3 + 180
4. in Quadrant 4: reference angle = 360 – angle in quadrant 4