input: Write a python function to check if three points are collinear.
  assert checkCollinearity((1,1), (2,2), (3,3)) == True
  assert checkCollinearity((1,2), (3,4), (5,6)) == True
  assert checkCollinearity((1,1), (2,3), (3,5)) == False
output: def checkCollinearity(p1, p2, p3):
      (x1, y1), (x2, y2), (x3, y3) = p1, p2, p3
      return (y2 - y1) * (x3 - x2) == (y3 - y2) * (x2 - x1)