The sum of the square of the modulus of the elements in the set \z = a + ib : a, b Z, z C, |z - 1| 1, |z - 5| |z - 5i|\ is .
Answer
9
Solution
[figure]
|z - 1| 1: the disc with centre (1, 0) and radius 1, whose integer points are 0, 1, 2, 1 + i, 1 - i.
|z - 5| |z - 5i|: z is nearer to (5, 0) than to (0, 5), i.e. on or below the bisector y = x (b a).
All five points satisfy b a (shaded region), so
|z|2 = 0 + 1 + 4 + 2 + 2 = 9
Answer: 9