Three points A, B and C are placed on a horizontal road, with B somewhere between A and C.
(i) State the relationship that must hold between the three distances AB, BC and AC when the three points lie on exactly the same straight line.
(ii) Give a clear explanation (without using the idea of the slope of a line) of why the statement in part (i) is true.
(iii) Choose any three suitable coordinates for A and C. Select a point B that lies between them, calculate AB, BC and AC, and show numerically that your result illustrates the statement from part (i).