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Let $z=1+i$ and $z_{1}=\frac{1+i \bar{z}}{\bar{z}(1-z)+1 / z}$. Then $\frac{12}{\pi} \arg \left(z_{1}\right)$ is equal to \_\_\_\_.

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  • #12372
    UPLIFTJEE
    Keymaster

    Let $z=1+i$ and $z_{1}=\frac{1+i \bar{z}}{\bar{z}(1-z)+1 / z}$. Then $\frac{12}{\pi} \arg \left(z_{1}\right)$ is equal to \_\_\_\_.
    [JEE (Main) 30 Jan 2023 S I]

    #12373
    UPLIFTJEE
    Keymaster

    Solution

    $\mathrm{z}=1+\mathrm{i} \Rightarrow \mathrm{z}_{1}=\frac{1+\mathrm{i} \overline{\mathrm{z}}}{\overline{\mathrm{z}}(1-\mathrm{z})+1 / \mathrm{z}} \Rightarrow \mathrm{z}_{1}=\frac{1+\mathrm{i}(1-\mathrm{i})}{(1-\mathrm{i})(1-1-\mathrm{i})+\frac{1}{1+\mathrm{i}}}$

    \[ \begin{aligned} & =\frac{1+\mathrm{i}-\mathrm{i}^{2}}{(1-\mathrm{i})(-\mathrm{i})+\frac{1-\mathrm{i}}{2}}=\frac{2+\mathrm{i}}{-\frac{3 \mathrm{i}-1}{2}}=\frac{4+2 \mathrm{i}}{-3 \mathrm{i}-1}=-\frac{(4+2 \mathrm{i})(3 \mathrm{i}-1)}{(3 \mathrm{i})^{2}-(1)^{2}}=-1+\mathrm{i} \\ & \operatorname{Arg}\left(\mathrm{z}_{1}\right)=\pi-\frac{\pi}{4}=\frac{3 \pi}{4} \therefore \frac{12}{\pi} \arg \left(\mathrm{z}_{1}\right)=\frac{12}{\pi} \times \frac{3 \pi}{4}=9 \end{aligned} \]
    #12374
    UPLIFTJEE
    Keymaster

    Answer

    9

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