Medium MCQ +4 / -1 PYQ · JEE Mains 2021

If the equation $a|z{|^2} + \overline {\overline \alpha z + \alpha \overline z } + d = 0$ represents a circle where a, d are real constants then which of the following condition is correct?

  1. A |$\alpha$|<sup>2</sup> $-$ ad $\ne$ 0
  2. B |$\alpha$|<sup>2</sup> $-$ ad &gt; 0 and a$\in$R $-$ {0} Correct answer
  3. C |$\alpha$|<sup>2</sup> $-$ ad $\ge$ 0 and a$\in$R
  4. D $\alpha$ = 0, a, d$\in$R<sup>+</sup>

Solution

$a|z{|^2} + \alpha \overline z + \overline \alpha z + d = 0$<br><br>$\Rightarrow$ $$z\overline z + \left( {{\alpha \over a}} \right)\overline z + \left( {{{\overline \alpha } \over a}} \right)z + {d \over a} = 0$$<br><br>$\therefore$ Centre $= - {\alpha \over a}$<br><br>$r = \sqrt {{{\left| {{\alpha \over a}} \right|}^2} - {d \over a}}$<br><br>$\Rightarrow {\left| {{\alpha \over a}} \right|^2} \ge {d \over a}$<br><br>$\Rightarrow {\left| \alpha \right|^2} \ge ad$

About this question

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

This question is part of PrepWiser's free JEE Main question bank. 223 more solved questions on Complex Numbers and Quadratic Equations are available — start with the harder ones if your accuracy is >70%.

Drill 25 more like these. Every day. Free.

PrepWiser turns these solved questions into a daily practice loop. Chapter-wise drills, full mocks, AI doubt chat. No auto-renew.

Start free →