If we consider the complex numbers z1, z2 and z3 to be the points corresponding to A,B and C, then
Since z1, z2 and z3 are gievn to be in A.P., hence by definition we have,
2z2 = z1 + z3
Hence, this means z2 = (z1 + z3) / 2
This means that B is the mid point of line AC.
We can say that A, B and C are collinear.
This means that the points z1, z2 and z3 lie on a line.
Thanks & Regards
Latika Leekha
askIITians Faculty