To get the reference angle π/6 for the given angles we will check each angle given in the options. A. 8π/6 Since 8π/6 means 240° which lies in 3rd quadrant. Therefore reference angle of 240°= 240-180 = 60° or π/3 B. 13π/6 13π/6 means 390° which lies in first quadrant. Therefore reference angle = 390-360 = 30° or π/6 C. 3π/6 Since 3π/6 means 90° therefore reference angle of 90° is the same as 90°. Or the reference angle is = π/2 D. 5π/6 5π/6 means angle is 150° which lies in second quadrant therefore reference angle of 150° = 180-150 = 30° or π/6 answer is Option B and D.
