Let A = \z C : |z - 2 - i| = 3\, B = \z C : Re(z - iz) = 2\ and S = A B. Then z S |z|2 is equal to .
Answer
22
Solution
Let z = x + iy.
A: |z - (2 + i)| = 3 (x - 2)2 + (y - 1)2 = 9
B: z - iz = (x + iy) - i(x + iy) = (x + y) + i(y - x)
Re(z - iz) = x + y = 2 y = 2 - x
Substituting in A: (x - 2)2 + (1 - x)2 = 9
2x2 - 6x - 4 = 0 x2 - 3x - 2 = 0
Two points: x1 + x2 = 3, x1x2 = -2 x12 + x22 = 9 + 4 = 13
|z|2 = x2 + (2 - x)2 = 2x2 - 4x + 4
|z|2 = 2(x12 + x22) - 4(x1 + x2) + 8
= 26 - 12 + 8 = 22
Answer: 22