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Question 40 — JEE (Main) 13 April 2023 Sii

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  • #11853
    Om Sharma
    Keymaster

    Let $S=\left\{z \in C: \bar{z}=i\left(z^{2}+\operatorname{Re}(\bar{z})\right)\right\}$. Then $\sum_{z \in S}|z|^{2}$ is equal to [JEE (Main) 13 April 2023 SII]
    (A) $\frac{5}{2}$
    (B) 4
    (C) $\frac{7}{2}$
    (D) 3

    #11854
    Om Sharma
    Keymaster

    Solution

    Let $\mathrm{Z}=\mathrm{x}+\mathrm{iy}, \mathrm{x} \in \mathrm{R}, \mathrm{y} \in \mathrm{R} \Rightarrow \mathrm{x}-\mathrm{iy}=\mathrm{i}\left(\mathrm{x}^{2}-\mathrm{y}^{2}+(2 \mathrm{xy}) \mathrm{i}+\mathrm{x}\right)$
    $\mathrm{x}=-2 \mathrm{xy} \ldots(1) \Rightarrow-\mathrm{y}=-\mathrm{y}^{2}+\mathrm{x}^{2}+\mathrm{x} \quad \ldots(2) \Rightarrow \mathrm{x}=0, \mathrm{y}=-\frac{1}{2}$ (from (1))
    If $\mathrm{x} \neq 0$, then $\mathrm{y}=0,1 \Rightarrow$ If $\mathrm{y}=-\frac{1}{2}$, then $\mathrm{x}=\frac{1}{2},-\frac{3}{2} \Rightarrow \mathrm{Z}=0+\mathrm{i} 0,0+\mathrm{i}, \frac{1}{2}-\frac{\mathrm{i}}{2},-\frac{3}{2}-\frac{\mathrm{i}}{2}$

    #11855
    Om Sharma
    Keymaster

    Answer

    D

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