Question: What is the reference angle for 2pi/3?

Answer: pi/3

Question: What is the reference angle for 11pi/7?

Answer: 3pi/7

Question: What is the reference angle for pi/4?

Answer: pi/4

Question: What is the reference angle for 7pi/4?

Answer: pi/4

Question: What is the reference angle for pi?

Answer: does not exist