Mathematics · Complex Numbers

JEE Main 2024 — 1 February, Shift 1 — Question 6

Let S={z∈C:∣z−1∣=1S=\{z \in C:|z-1|=1 and (2−1)(z+zˉ)−i(z−zˉ)=22}(\sqrt{2}-1)(z+\bar{z})-i(z-\bar{z})=2 \sqrt{2}\}. Let z1,z2z_{1}, \quad z_{2} ∈S\in S be such that ∣z1∣=max⁡z∈S∣z∣\left|z_{1}\right|=\max _{z \in S}|z| and ∣z2∣=min⁡z∈S∣z∣\left|z_{2}\right|=\min _{z \in S}|z|. Then ∣2z1−z2∣2\left|\sqrt{2} z_{1}-z_{2}\right|^{2} equals :

  1. Option A:

    1

  2. Option B:

    4

  3. Option C:

    3

  4. Option D:

    2

    Correct

Answer: D

Step-by-step solution

Let Z=x+iy\mathrm{Z}=\mathrm{x}+\mathrm{iy}

Then (x−1)2+y2=1→(1)(\mathrm{x}-1)^{2}+\mathrm{y}^{2}=1 \quad \rightarrow(1)

&(2−1)(2x)−i(2iy)=22⇒(2−1)x+y=2→(2)\begin{aligned} \& & (\sqrt{2}-1)(2 x)-i(2 i y)=2 \sqrt{2} & \Rightarrow(\sqrt{2}-1) x+y=\sqrt{2} \rightarrow(2)\end{aligned}

Solving (1) & (2) we get Either x=1x=1 or x=12−2→(3)x=\frac{1}{2-\sqrt{2}} \rightarrow(3)

On solving (3) with (2) we get For

x=1⇒y=1⇒Z2=1+i\mathrm{x}=1 \Rightarrow \mathrm{y}=1 \Rightarrow Z_{2}=1+i $

for x=12−2⇒y=2−12⇒Z1=(1+12)+i2x=\frac{1}{2-\sqrt{2}} \Rightarrow y=\sqrt{2}-\frac{1}{\sqrt{2}} \Rightarrow Z_{1}=\left(1+\frac{1}{\sqrt{2}}\right)+\frac{i}{\sqrt{2}}

Now ∣2z1−z2∣2\left|\sqrt{2} z_{1}-z_{2}\right|^{2}

=∣(12+1)2+i−(1+i)∣2=\left|\left(\frac{1}{\sqrt{2}}+1\right) \sqrt{2}+i-(1+i)\right|^{2}

=(2)2=(\sqrt{2})^{2}

=2=2

Answer key and solution verified before publishing.

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Exam
JEE Main 2024
Subject
Mathematics
Chapter
Complex Numbers
Topic
Conjugate of complex numbers & properties