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Let $\mathrm{z}_{1}, \mathrm{z}_{2} \in \mathrm{C}$ be the distinct solutions of the equation $\mathrm{z}^{2}+4 \mathrm{z}-(1+12 \mathrm{i})=0$.

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  • #12279
    UPLIFTJEE
    Keymaster

    Let $\mathrm{z}_{1}, \mathrm{z}_{2} \in \mathrm{C}$ be the distinct solutions of the equation $\mathrm{z}^{2}+4 \mathrm{z}-(1+12 \mathrm{i})=0$.
    Then $\left|\mathrm{z}_{1}\right|^{2}+\left|\mathrm{z}_{2}\right|^{2}$ is equal to
    [JEE MAIN 05 April 2026 S II]
    (A) 18
    (B) 22
    (C) 29
    (D) 34

    #12280
    UPLIFTJEE
    Keymaster

    Solution

    $\mathrm{z}^{2}+4 \mathrm{z}-(1+12 \mathrm{i})=0$.

    \[ \begin{aligned} & \Rightarrow \mathrm{z}=\frac{-4 \pm \sqrt{16+4(1+12 \mathrm{i})}}{2}=-2 \pm \sqrt{5+12 \mathrm{i}} \\ & \because \sqrt{5+12 \mathrm{i}}=\mathrm{x}+\mathrm{iy} \text { where } \mathrm{x}, \mathrm{y} \in \mathrm{R} \\ & \Rightarrow 5+12 \mathrm{i}=\mathrm{x}^{2}-\mathrm{y}^{2}+2 \mathrm{xyi} \\ & \Rightarrow 2 \mathrm{xy}=12 \Rightarrow \mathrm{y}=\frac{6}{\mathrm{x}} \& \mathrm{x}^{2}-\mathrm{y}^{2}=5 \\ & \Rightarrow \mathrm{x}^{2}-\frac{36}{\mathrm{x}^{2}}=5 \Rightarrow \mathrm{x}^{4}-5 \mathrm{x}^{2}-36=0 \\ & \Rightarrow\left(\mathrm{x}^{2}-9\right)\left(\mathrm{x}^{2}+4\right)=0 \Rightarrow \mathrm{x}^{2}=-4 \Rightarrow \mathrm{x}= \pm 2 \mathrm{i} \text { (rejected) } \\ & \Rightarrow \mathrm{x}^{2}=9 \Rightarrow \mathrm{x}= \pm 3 ; \mathrm{y}=\frac{6}{\mathrm{x}}= \pm 2 \\ & \because \sqrt{5+12 \mathrm{i}}= \pm(3+2 \mathrm{i}) \end{aligned} \]
    \[ \begin{aligned} & \Rightarrow z=-2 \pm(3+2 i) \Rightarrow z=1+2 i,-5-2 i \\ & \therefore\left|z_{1}\right|^{2}+\left|z_{2}\right|^{2}=(1+4)+(25+4)=5+29=34 \end{aligned} \]
    #12281
    UPLIFTJEE
    Keymaster

    Answer

    D

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