A complex number z is said to be unimodular if . Suppose `z_1` and `z_2` are complex numbers such that `(z_1-2z_2)/(2-z_1z_2)` is unimodular and `z_2` is not unimodular. Then the point `z_1` lies on a : (1) straight line parallel to x-axis (2) straight line parallel to y-axis (3) circle of radius 2 (4) circle of radius `sqrt(2)`