Find the angle’s quadrant
Use the angle itself if it is in Quadrant I
Use 180° minus the angle if it is in Quadrant II
Use the angle minus 180° if it is in Quadrant III
Use 360° minus the angle if it is in Quadrant IV
For angles in radians, use π minus the angle in Quadrant II
For angles in radians, use the angle minus π in Quadrant III
For angles in radians, use 2π minus the angle in Quadrant IV
Make sure the reference angle is always positive and less than 90° or π/2