Tion vectors of the points a, b and c are
a = 3i - j - k, b = 2i + 2j + 7k and c = 5i + 2j - 3k.
find
(i) the position vector of the centroid of a, b and c.
(ii) the position vectors of the points p and q which divide ab internally and externally in the ratios ap : pb = 1 : 2 and aq : qb = -2 : 1
