Ответ на вопрос: 1. (b) OABC is a trapezium, where OA is parallel to CB. M is the midpoint of CB, and N is a point on AB such that AN : NB = 1 : 2. O is the origin, OA = p, OC = q and CB = r. (i) Find, in terms of p, q and r: (a) OB; (b) AB; (c) MN. (ii) OA and MN intersect at G. Find the position vector of G in terms of p.