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Question 26 — JEE (Main) 8 April 2024 (S I)

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  • #11811
    Om Sharma
    Keymaster

    Let z be a complex number such that $|z+2|=1$ and $\operatorname{Im}\left(\frac{z+1}{z+2}\right)=\frac{1}{5}$. Then the value of $|\operatorname{Re}(\overline{z+2})|$ is [JEE (Main) 8 April 2024 S I]
    (A) $\frac{2 \sqrt{6}}{5}$
    (B) $\frac{24}{5}$
    (C) $\frac{\sqrt{6}}{5}$
    (D) $\frac{1+\sqrt{6}}{5}$

    #11812
    Om Sharma
    Keymaster

    Solution

    $|\mathrm{z}+2|=1$ Let $\mathrm{z}+2=\cos \theta+\mathrm{i} \sin \theta \Rightarrow \overline{\mathrm{z}+2}=\frac{1}{\mathrm{z}+2}=\cos \theta-\mathrm{i} \sin \theta$

    \[ \begin{aligned} & \Rightarrow \frac{z+1}{z+2}=1-\frac{1}{z+2}=1-(\cos \theta-i \sin \theta)=(1-\cos \theta)-i \sin \theta \\ & \operatorname{Im}\left(\frac{z+1}{z+2}\right)=\sin \theta=\frac{1}{5} \Rightarrow \cos \theta= \pm \sqrt{1-\frac{1}{25}}= \pm \frac{2 \sqrt{6}}{5} \Rightarrow|\operatorname{Re}(\overline{z+2})|=|\cos \theta|=\frac{2 \sqrt{6}}{5} \end{aligned} \]
    #11813
    Om Sharma
    Keymaster

    Answer

    A

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