Let z be a complex number such that |z| = 1. If 2 + k2 zk + z = kz, k R, then the maximum distance of k + ik2 from the circle |z - (1 + 2i)| = 1 is :
- 5 + 1
- 3
- 3 + 1
- 2
Answer
(1) 5 + 1
Solution
|z| = 1, we have z = 1z, so the given relation becomes
2 + k2zk + 1z = kz z(2 + k2z)kz + 1 = kz
2z + k2z2 = k2z2 + kz
2z = kz, and since z 0, k = 2.
Hence k + ik2 = 2 + 4i, i.e. the point (2, 4).
The circle has centre (1, 2) and radius 1, and the distance of (2, 4) from the centre is 12 + 22 = 5 > 1, so the point lies outside the circle.
Maximum distance from the circle = 5 + 1
Answer: (1)