Option B. 13π/6 and Option D. 5π/6
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.