from math import *

def Cosinus(xA,yA,xB,yB,xC,yC):
    c=(xB-xA)**2+(yB-yA)**2
    b=(xC-xA)**2+(yC-yA)**2
    a=(xC-xB)**2+(yC-yB)**2
    cos=(b+c-a)/(2*sqrt(b*c))
    return cos