Let z be a complex number such that the real part of z - 2iz + 2i is zero. Then, the maximum value of |z - (6 + 8i)| is equal to
- 8
- 12
- 10
Answer
(2) 12
Solution
Put z = x + iy. Then z - 2iz + 2i = x + i(y - 2)x + i(y + 2), whose real part is x2 + (y - 2)(y + 2)x2 + (y + 2)2.
Real part = 0 gives x2 + y2 = 4, so z lies on the circle |z| = 2.
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|z - (6 + 8i)| is the distance of z from Q(6, 8), and OQ = 10.
It is greatest at M, the end of the diameter on the far side of Q, so maximum = 10 + 2 = 12.
Answer: (2)