Determine the angle between ä-(5, 3.0) and 6-(-1,0, 8) [3 Marks] 21. The vertices of a quadrilateral are A = [0, 3,5], B = (-3,-1,17], C= [4,-3,15] & D = [7.1,3]. Prove that ABCD is a parallelogram. [5 Marks]