mycroft holmes
Last Activity: 8 Years ago
z’ = 1+5z and so z’+1 = 5z which means |z’+1| = 5|z| = 10 which means z’ lies on a circle centred at (-1,0) and radius 10.
Alternatively you can see that 5z takes all points on the circle |z| =2 to the circle |z|=10 (it expands the circle). Then 5z -1 is simply displacing the circle left by 1 unit...so the figure remains a circle. This has the advantage of noticing that the whole process is reversible – you can map points on both circles bijectively to each other