• ValueError: math domain error

Question related to mission The Angles of a Triangle

 

My code:

from math import (pi, acos)   
def checkio(a, b, c):
  if a<b+c:
    alpha=round(math.acos((b**2+c**2-a**2)/2*b*c)*180/math.pi)
    betta=round(math.acos((a**2+c**2-b**2)/2*a*c)*180/math.pi)
    gamma=180-(alpha-betta)
    return sorted(list(alpha,betta,gamma))
 else:
    return [0, 0, 0]

what is wrong with the import?