Jee Mains

Question 7 — JEE Main 22 Jan 2026 S Ii

Viewing 3 posts - 1 through 3 (of 3 total)
  • Author
    Posts
  • #11754
    Om Sharma
    Keymaster

    Let $\mathrm{S}=\left\{\mathrm{z} \in \mathrm{C}: 4 \mathrm{z}^{2}+\overline{\mathrm{z}}=0\right\}$. Then $\sum_{\mathrm{z} \in \mathrm{S}}|\mathrm{z}|^{2}$ is equal to [JEE MAIN 22 Jan 2026 S II]
    (A) $\frac{3}{16}$
    (B) $\frac{7}{64}$
    (C) $\frac{1}{16}$
    (D) $\frac{5}{64}$

    #11755
    Om Sharma
    Keymaster

    Solution

    let $\mathrm{z}=\mathrm{x}+\mathrm{iy}, 4 \mathrm{z}^{2}+\overline{\mathrm{z}}=0 \Rightarrow 4(\mathrm{x}+\mathrm{iy})^{2}+(\mathrm{x}-\mathrm{iy})=0$

    \[ \begin{aligned} & \Rightarrow 4\left(x^{2}-y^{2}+2 x y i\right)+x-i y=0 \Rightarrow 4 x^{2}-4 y^{2}+x+i y(8 x-1)=0+i 0 \Rightarrow 4 x^{2}-4 y^{2}+x=0 \text { and } y(8 x-1)=0 \\ & \text { Case I: } y=0 ; 4 x^{2}-0+x=0 \Rightarrow x=0,-\frac{1}{4} \Rightarrow \Rightarrow Z_{1}=0+i 0, Z_{2}=-\frac{1}{4}+i 0 \Rightarrow\left|z_{1}\right|^{2}=0 ;\left|z_{2}\right|^{2}=\frac{1}{16} \\ & \text { Case II: } 8 x-1=0 \Rightarrow x=\frac{1}{8} \Rightarrow 4 x^{2}-4 y^{2}+x=0 \Rightarrow \frac{4}{64}-y^{2}+\frac{1}{8}=0 \Rightarrow 4 y^{2}=\frac{3}{16} \Rightarrow y= \pm \frac{\sqrt{3}}{8} \\ & z_{3}=\frac{1}{8}+\frac{\sqrt{3}}{8} i, z_{4}=\frac{1}{8}-\frac{\sqrt{3}}{8} i \Rightarrow\left|z_{3}\right|^{2}=\frac{1}{64}+\frac{3}{64}=\frac{1}{16} ;\left|z_{4}\right|^{2}=\frac{1}{64}+\frac{3}{64}=\frac{1}{16} \therefore \sum_{i=1}^{n}\left|z_{i}\right|^{2}=0+\frac{1}{16}+\frac{1}{16}+\frac{1}{16}=\frac{3}{16} \end{aligned} \]
    #11756
    Om Sharma
    Keymaster

    Answer

    A

Viewing 3 posts - 1 through 3 (of 3 total)
  • You must be logged in to reply to this topic.