Mathematics · Complex Numbers

JEE Main 2026 — 6 April, Morning Shift — Question 24

Let the set of all values of k∈R such that the equation z(zˉ+2+i)+k(2+3i)=0z(\bar{z}+2+i)+k(2+3i)=0, z∈C,z∈C, has at least one solution, be the interval [α,β].[α,β]. Then 9(α+β)9(α+β) is equal to:

  1. Option A:

    −10-10

    Correct
  2. Option B:

    −8-8

  3. Option C:

    101310\sqrt{13}

  4. Option D:

    8138\sqrt{13}

Answer: A

Step-by-step solution

Put z=x+iy,z‾=x−iy\mathrm{z}=\mathrm{x}+\mathrm{iy}, \overline{\mathrm{z}}=\mathrm{x}-\mathrm{iy} ⇒z‾+2+i=x−iy+2+i\Rightarrow \overline{\mathrm{z}}+2+\mathrm{i}=\mathrm{x}-\mathrm{iy}+2+\mathrm{i} ⇒z(z‾+2+i)=(x+iy)(x+2+i(1−y))\Rightarrow \mathrm{z}(\overline{\mathrm{z}}+2+\mathrm{i})=(\mathrm{x}+\mathrm{iy})(\mathrm{x}+2+\mathrm{i}(1-\mathrm{y})) ⇒ Real part =x(x+2)−y(1−y)=\mathrm{x}(\mathrm{x}+2)-\mathrm{y}(1-\mathrm{y}) Imaginary part =x(1−y)+y(x+2)=x(1-y)+y(x+2)

\Rightarrow x^{2}+y^{2}+2 x-y+2 k=0 \end{gathered}$$ and $\mathrm{x}+2 \mathrm{y}+3 \mathrm{k}=0$ eliminating $x$ from (1) and (2) $5 \mathrm{y}^{2}+(12 \mathrm{k}-5) \mathrm{y}+9 \mathrm{k}^{2}-4 \mathrm{k}=0$ since $y \in R$ use $\mathrm{D} \geq 0$ $(12 \mathrm{k}-5)^{2}-4.5\left(9 \mathrm{k}^{2}-4 \mathrm{k}\right) \geq 0$ $\Rightarrow 36 \mathrm{k}^{2}+40 \mathrm{k}-25 \leq 0$ $\Rightarrow \alpha+\beta=\frac{-10}{9}$ $\Rightarrow 9(\alpha+\beta)=-10$

Answer key and solution verified before publishing.

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Exam
JEE Main 2026
Subject
Mathematics
Chapter
Complex Numbers
Topic
Introduction to Complex Numbers
Let the set of all values of k∈R such that the equation z(bar z… | JEE Main 2026 PYQ with Solution · DhiX AI