Consider the x-y plane. Given that the points (0,0), (0,1), and (1,0) belong to the set R and that the point (1,1) belongs to set S. What is the equation of a straight line (i.e., ax + by = k) which separates sets R and S (i.e., all points of R are on one side of the boundary line and all points of S are on the other side.)