18. What is the domain, D, and the range, R, of the relation defined by: [(3, 7), (3, 5), (3, 6), (3, 2)) a) D (2, 3, 5, 6, 7} c) D= {3} R (2, 3, 5, 6, 7} R={2, 5, 6, 7} b) D= {2, 5, 6, 7} d) D={3} R={3} R = {2, 7} 19. Which of the following does not represent a function? a) {(2, 2)} b) {(1, 3), (2, 5), (2, 7), (3, 9)} 20. Which of the following relations are functions? c) ((5, 1), (-2, 1), (4, 1)) d) {(1, 1), (2, 2), (3, 3), (4, 4)} I II a) I and IV only b) II and III only c) I and II only d) III only 21. What are the coordinates of point A? a) (2,-4) b) (-4,2) c) (4,-2) d) (-2, 4) III IV >