જો \(z\,\ne -i\) એ એવી સંકર સંખ્યા હોય કે જેથી \(\frac{{z - i}}{{z + i}}\) એ શુધ્ધ કાલ્પનિક સંખ્યા થાય તો \(z +\frac {1}{z}\) ની કિમત મેળવો.

A \(0\)
B \(1\) સિવાયની કોઈક શૂન્યેતર વાસ્તવિક સંખ્યા મળે.
C કોઈક શૂન્યેતર વાસ્તવિક સંખ્યા મળે.
D શુધ્ધ કાલ્પનિક સંખ્યા

Verified Solution

Answer & Solution

Correct Answer

(C) કોઈક શૂન્યેતર વાસ્તવિક સંખ્યા મળે.

Step-by-step Solution

Detailed explanation

Let \(z=x+i y\) \(\frac{z-i}{z+i}\) is purely imaginary means its real part is zero. \(\frac{x+i y-i}{x+i y+i}=\frac{x+i(y-1)}{x+i(y+1)} \times \frac{x-i(y+1)}{x-i(y+1)}\) \({ = \frac{{{x^2} - 2ix(y + 1) + xi(y - 1) + {y^2} - 1}}{{{x^2} + {{(y + 1)}^2}}}}\)…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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