Let a and b be non-zero parallel vectorsand let the points A,B,C and D be given by OA=a, OB=b, OC= 3a-b,OD = -a+2b a) express the vectors AB,AC,AD,BC,BD and CD in terms of a and b. b) Find, in terms of a and b, vectors from the origin to the midpoints of the line segments AB and CD. 3. The attempt at a solution a) AB = b-a AC = (3a-b)-a = 2a-b AD = (-a+2b)-a = -2a+2b BC = (3a-b)-b = 3a-2b BD = (-a+2b)-b = -a+b (-a+2b)-(3a-b) = -4a+b Hope it's right. b) I don't know how to do question. I appreciate it if someone could give me some guidance and show me how to solve this question. Thanks!