Medium MCQ +4 / -1 PYQ · JEE Mains 2023

For all $z \in C$ on the curve $C_{1}:|z|=4$, let the locus of the point $z+\frac{1}{z}$ be the curve $\mathrm{C}_{2}$. Then :

  1. A the curves $C_{1}$ and $C_{2}$ intersect at 4 points Correct answer
  2. B the curve $C_{2}$ lies inside $C_{1}$
  3. C the curve $C_{1}$ lies inside $C_{2}$
  4. D the curves $C_{1}$ and $C_{2}$ intersect at 2 points

Solution

Let $\mathrm{w}=\mathrm{z}+\frac{1}{\mathrm{z}}=4 \mathrm{e}^{\mathrm{i} \theta}+\frac{1}{4} \mathrm{e}^{-\mathrm{i} \theta}$ <br/><br/>$\Rightarrow \mathrm{w}=\frac{17}{4} \cos \theta+\mathrm{i} \frac{15}{4} \sin \theta$ <br/><br/>So locus of $w$ is ellipse $\frac{x^{2}}{\left(\frac{17}{4}\right)^{2}}+\frac{y^{2}}{\left(\frac{15}{4}\right)^{2}}=1$ <br/><br/>Locus of $\mathrm{z}$ is circle $\mathrm{x}^{2}+\mathrm{y}^{2}=16$ <br/><br/>So intersect at 4 points.

About this question

Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane

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