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NDA 2021 Maths · Mathematics · Complex Numbers and Quadratic Equations · easy

For any complex number z, |z|^2=zbar z. 2. For any non-zero complex number z, |(z)/(bar z)|=1.

Single correct option

Which of the statements is/are correct? 1. For any complex number zz, ∣z∣2=zzˉ|z|^2=z\bar z. 2. For any non-zero complex number zz, ∣zzˉ∣=1\left|\dfrac{z}{\bar z}\right|=1.
  1. A. 1 only
  2. B. 2 only
  3. C. Both 1 and 2
  4. D. Neither 1 nor 2
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Answer: (C) Both 1 and 2

Statement 1 is the definition-based identity zzˉ=x2+y2=∣z∣2z\bar z=x^2+y^2=|z|^2. Statement 2 holds because ∣zˉ∣=∣z∣|\bar z|=|z|, so the ratio of moduli is 11 for every non-zero zz. Both are correct.
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Original question written in the NDA 2021 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake