Three points are given by A(1,2,−1), B(4,8,5) and C(7,14,k) where k is a real parameter.
a. (i) Find the value of k for which the vectors AB and AC are parallel.
b. (ii) For the value of k obtained in part (i), prove that the points A,B and C are collinear and specify whether B lies between A and C.
c. (iii) Determine the ratio in which point B divides the line segment AC. (Express the ratio as AB:BC.)