90 degress= ? radians

Question

How is the answer pie over 2?
330 degrees = 11pie over 6
-105 degrees= -7pie over 12

Converting the angle in radians to degrees
3pie over 4 =135 degrees
pie over 2 = 90 degrees

pie over 30 = 6 degrees

-7pie over 5 =-135 degrees

I have these answers but I have no idea on how to get them..

Answer 1

180o = pi Radians.
Divide both sides by 2:
900 = p1/2 Radians.

OR

piRad/180Deg * 90Deg = 90pi/180=pi/2.

piRad/180Deg * 330Deg = 330pi/180=11pi/6