Just a couple of questions, if anyone would be so kind to help:
1. Prove that the three points: z1, z2 and z3 are collinear, if and only if the ration (z3-z1) / (z2-z1) is real. Hence show the points 5 + 8i, 13+20i and 19 + 29i.
I think I know how to do the second bit, just gradient, right...