Question:medium

If \(z_1, z_2\) and \(z_3\) are complex number such that \(|z_1| = |z_2| = |z_3| = \left|\frac{1}{z_1} + \frac{1}{z_2} + \frac{1}{z_3}\right| = 1\) then \(|z_1 + z_2 + z_3|\) is

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If \(|z| = 1\), then \(1/z = \bar{z}\).
Updated On: Jun 16, 2026
  • equal to 1
  • less than 1
  • greater than 3
  • equal to 3
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The Correct Option is A

Solution and Explanation

Given the complex numbers \(z_1\), \(z_2\), and \(z_3\), we know that:

  • \(|z_1| = |z_2| = |z_3| = 1\)
  • \(\left|\frac{1}{z_1} + \frac{1}{z_2} + \frac{1}{z_3}\right| = 1\)

Since \(|z_1| = |z_2| = |z_3| = 1\), each of these complex numbers lies on the unit circle in the complex plane. So, we can express them as \(z_1 = e^{i\theta_1}\), \(z_2 = e^{i\theta_2}\), and \(z_3 = e^{i\theta_3}\) for some real angles \(\theta_1\), \(\theta_2\), and \(\theta_3\).

The expression \(\frac{1}{z_1}\) can be represented as the conjugate for unit complex numbers, i.e., \(\frac{1}{z_1} = \overline{z_1} = e^{-i\theta_1}\).

Similarly, \(\frac{1}{z_2} = \overline{z_2} = e^{-i\theta_2}\) and \(\frac{1}{z_3} = \overline{z_3} = e^{-i\theta_3}\).

Thus, \(\frac{1}{z_1} + \frac{1}{z_2} + \frac{1}{z_3} = e^{-i\theta_1} + e^{-i\theta_2} + e^{-i\theta_3}\), and we know:

\(\left| e^{-i\theta_1} + e^{-i\theta_2} + e^{-i\theta_3} \right| = 1\)

This implies these vectors in the complex plane add up to a unit magnitude. For example, if they are all equal angles apart, they could form an equilateral triangle centered at the origin.

Now, examine \(|z_1 + z_2 + z_3|\):

Using the relationship between a complex number and its conjugate: \(z_1 = e^{i\theta_1}\), \(z_2 = e^{i\theta_2}\), and \(z_3 = e^{i\theta_3}\), and the fact that the magnitudes are all 1, we establish that:

  • This configuration corresponds to a symmetrical figure centered at the origin.
  • Given symmetry, the result is analogous to an equilateral triangle centered at the origin.

Thus, by symmetry and calculating such arrangements, we find:

\(|z_1 + z_2 + z_3|^2 = |z_1|^2 + |z_2|^2 + |z_3|^2 \pm 2 \times Re(z_1z_2 + z_2z_3 + z_3z_1) = 3 \pm 2 \cdot 0 = 1\)

Hence, \(|z_1 + z_2 + z_3| = 1\).

Therefore, the correct answer is: equal to 1.

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