(ii) Show that the set of points P(4,−1,2)P(4, -1, 2)P(4,−1,2), Q(1,3,−1)Q(1, 3, -1)Q(1,3,−1) and R(−2,4,6)R(-2, 4, 6)R(−2,4,6) form a right triangle.