The reference angle of θ is the acute angle θR that the terminal side of θ makes with the x-axis.
Choose a proper formula for calculating the reference angle:
0° to 90°: reference angle = angle ,
90° to 180°: reference angle = 180° - angle ,
180° to 270°: reference angle = angle - 180° ,
270° to 360°: reference angle = 360° - angle .
5.75rad × 180/π = 329.451°
The reference angle = 360- 329.451= 30.549
= 30.55 degrees.