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JEE Main 202116 MarchEvening Shift
Exam
JEE Main
Year
2021
Date
16 March
Shift
Evening Shift
Subject
Mathematics
Chapter
Complex Number

JEE Main 2021 · 16 March · Evening Shift · Mathematics · Complex Number

The least value of |z| where z is complex number which satisfies...

The least value of ∣z∣\left|z\right| where zz is complex number which satisfies the inequality e((∣z∣+3)(∣z∣−1)∣∣z∣+1∣log⁡e2)≥log⁡2∣57+9i∣{e}^{\left(\dfrac{\left(\left|z\right| + 3\right)\left(\left|z\right| - 1\right)}{\left|\left|z\right| + 1\right|}\log_{e}2\right)} \ge \log_{\sqrt{2}}\left|5\sqrt{7} + 9i\right|, i=−1,i = \sqrt{- 1}, is equal to :

Options

  1. A33
  2. B5\sqrt{5}
  3. C22
  4. D88

Correct answer

A. 33

Step-by-step solution

{e}^{\left(\dfrac{\left(\left|z\right| + 3\right)\left(\left|z\right| - 1\right)}{\left|\left|z\right| + 1\right|}\log_{e}2\right)} \ge \log_{\sqrt{2}}\left|5\sqrt{7} + 9i\right|</p><p></p><p>⇒ 2\dfrac{\left(\left|z\right| + 3\right)\left(\left|z\right| - 1\right)}{\left(\left|z\right| + 1\right)} \ge lo{g}_{\sqrt{2}}\left(16\right)</p><p></p><p>⇒ 2\dfrac{\left(\left|z\right| + 3\right)\left(\left|z\right| - 1\right)}{\left(\left|z\right| + 1\right)} \ge {2}^{3}</p><p></p><p>\dfrac{\left(\left|z\right| + 3\right)\left(\left|z\right| - 1\right)}{\left(\left|z\right| + 1\right)} \ge 3</p><p>(∣z∣+3)(∣z∣−1)≥3(∣z∣+1)</p><p>\left(\left|z\right| + 3\right)\left(\left|z\right| - 1\right) \ge 3\left(\left|z\right| + 1\right)

∣z∣2+2∣z∣−3≥3∣z∣+3{\left|z\right|}^{2} + 2\left|z\right| - 3 \ge 3\left|z\right| + 3

⇒∣z∣2+∣z∣−6≥0⇒ {\left|z\right|}^{2} + \left|z\right| - 6 \ge 0

⇒(∣z∣−3)(∣z∣+2)≥0⇒∣z∣−3≥0⇒ \left(\left|z\right| - 3\right)\left(\left|z\right| + 2\right) \ge 0 ⇒ \left|z\right| - 3 \ge 0

⇒ \left|z\right| \ge 3 ⇒ {\left|z\right|}_\min = 3

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