For this case, the first thing you should do is to know the following transformation:
pi radians = 180 degrees
Applying the transformation we have:
(13pi / 6) * (180 / pi) = 390 degrees
Then, in quadrant 1 we have:
390 - 360 = 30 degrees
Answer:
13 pi / 6 as a function of an angle in quadrant i is:
30 degrees