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JEE Advanced · Mathematics · 3. Complex Numbers

Paragraph:
Let \(A, B, C\) be three sets of complex numbers as defined below.
\(A=\{z ; \operatorname{lm} z \geq 1\} ; B=\{z:|z-2-i|=3\} ;\) \(C=\{z: \operatorname{Re}((1-i) z)=\sqrt{2}\}\).
Question:
Let \(z\) be any point in \(A \cap B \cap C\) and let \(w\) be any point satisfying \(|w-2-i| < 3\). Then, \(|z|-|w|+3\) lies between

  1. A \(-6\) and 3
  2. B \(-3\) and 6
  3. C \(-6\) and 6
  4. D \(-3\) and 9
Verified Solution

Answer & Solution

Correct Answer

(D) \(-3\) and 9

Step-by-step Solution

Detailed explanation

\(|w-(2+i)| < 3 \)
\( \Rightarrow \quad|| w|-| 2+i|| < 3 \)
\( \Rightarrow -3+\sqrt{5} < |w| < 3+\sqrt{5} \)
\( \Rightarrow -3-\sqrt{5} < -|w| < 3-\sqrt{5}\)
Also, \(|z-(2+i)|=3\)
\(\Rightarrow -3+\sqrt{5} \leq|z| \leq 3+\sqrt{5}\)
\(-3 < |z|-|w|+3 < 9\)
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