the measure of the smallest, positive, acute angle t formed by the terminal side of the angle t and the horizontal axis.
90° to 180°: reference angle = 180° - angle, 180° to 270°: reference angle = angle - 180, 270° to 360°: reference angle = 360° - angle.
if your given angle is 110°, then its reference angle is 180° – 110° = 70°. When the terminal side is in the third quadrant (angles from 180° to 270°) your reference angle is your given angle minus 180°. So, if your given angle is 214°, then its reference angle is 214° – 180° = 34°.
