i replace z with rcis(theta)
then do you move the other terms the the other side of the inequality and use them as asymptotes?
so it would become a circle radius 3r and asymptotes at 5 and -5i?
The reason this works is that geometrically (to use Mr F's word) is the distance between the points representing the complex numbers and . So if is a constant, will be the distance of the point representing z from a fixed point, which we can call A. This in turn is why the equation (where r is real) represents a circle, centre A, radius .