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AP EAMCET · Maths · Complex Number

If \(z\) is a complex number such that \(\frac{z-1}{z-i}\) is purely imaginary and locus of \(z\) represents a circle with centre \((\alpha, \beta)\) and radius \(r\), then \(\frac{\alpha}{\beta}+\frac{\beta}{\alpha}=\)

  1. A \(4 r\)
  2. B \(r^2\)
  3. C \(2 r^2\)
  4. D \(4 r^2\)
Verified Solution

Answer & Solution

Correct Answer

(D) \(4 r^2\)

Step-by-step Solution

Detailed explanation

Let \(z = x+iy\). \(Re\left(\frac{z-1}{z-i}\right) = 0\) \(Re\left(\frac{(x-1)+iy}{x+i(y-1)}\right) = 0\) \(\frac{x(x-1) + y(y-1)}{x^2+(y-1)^2} = 0\) \(x^2 - x + y^2 - y = 0\) \(\left(x - \frac{1}{2}\right)^2 + \left(y - \frac{1}{2}\right)^2 = \frac{1}{4} + \frac{1}{4}\)…