p^3=(z+x-y)/(y+z-x) * (x+y-z)/(z+x-y) * (y+z-x)/(x+y+z)= (x+y-z)/(x+y+z)p^2 = (y+z-x)/(x+y+z) * (z+x-y)/(y+z-x)= (z+x-y)/(z+x+y)p = (y+z-x)/(x+y+Z)p^3+p^2+p= (x+y-z+z+x-y+z-x+y)/(z+x+y)= 1
