(a) If O is in standard position, then the reference angle ő is the acute angle formed by the terminal side of O and the --Select-- v. So the reference angle for 0 = 100° is = that for 0 = 200° is and (b) If 0 is any angle, the value of a trigonometric function of 0 is the same, except possibly for sign, as the value of the trigonometric function of O. So sin(100°) = sin( sin(200°) .). = -sin ()