MCQ
If $\mathrm{S}=\left\{\mathrm{z} \in \mathbb{C}: \frac{\mathrm{z}-i}{\mathrm{z}+2 i} \in \mathbb{R}\right\}$, then :
  • A
    $S$ contains exactly two elements
  • B
    $S$ contains only one element
  • C
    $\mathrm{S}$ is a circle in the complex plane
  • $\mathrm{S}$ is a straight line in the complex plane

Answer

Correct option: D.
$\mathrm{S}$ is a straight line in the complex plane
d
Given $\frac{\mathrm{z}-\mathrm{i}}{\mathrm{z}+2 \mathrm{i}} \in \mathrm{R}$

Then $\arg \left(\frac{\mathrm{z}-\mathrm{i}}{\mathrm{z}+2 \mathrm{i}}\right)$ is $0$ or $\Pi$

$\Rightarrow \mathrm{S}$ is straight line in complex

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