4. Double-angle Formulas 2 tan 0 sin (20) = 2 sin 0 cos 0; tan (20) = 1 - tan2 0 cos (20) = cos2 0 - sin2 0 = 1 - 2 sin2 0 = 2 cos2 0 - 1 Half-angle Formulas - cos 0 1 + cos 0 sin NI O = =1 COS = : 2 2 1 - cos 1 - cos 0 sin 0 tan = =1 1 + cos 0 sin 0 1 + cos 0 where the + or - sign is determined by the quadrant of the angle , Answer the following questions. 3 (a Given cost = and -7