When an angle is drawn on the coordinate plane with a vertex at the origin, the reference angle is the angle between the terminal side of the angle and the x-axis.
Sketching our angle, we have
The blue angle represents the reference angle and the red angle represents our angle.
The blue angle is the difference between 250º and 180º.
[tex]250^o-180^o=70^o[/tex]The reference angle is 70º.
