Question:medium

If \(\mathbf{a} \times \mathbf{b} = \mathbf{c}\), \(\mathbf{b} \times \mathbf{c} = \mathbf{a}\) and \(a, b, c\) be the moduli of the vectors \(\mathbf{a}, \mathbf{b}, \mathbf{c}\) respectively, then

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If \(\mathbf{u} \times \mathbf{v} = \mathbf{w}\), then all three vectors are mutually perpendicular.
Updated On: Jun 19, 2026
  • \(a = 1, b = 1, c = 1\)
  • \(a = 1, b = 1, c = a\)
  • \(a = c, b = 1\)
  • \(a = 1, b = c\)
Show Solution

The Correct Option is D

Solution and Explanation

To solve the problem, let's analyze the given vector equations and find the relationship between the magnitudes of the vectors involved.

  1. Given: \(\mathbf{a} \times \mathbf{b} = \mathbf{c}\) and \(\mathbf{b} \times \mathbf{c} = \mathbf{a}\). This implies that \(\mathbf{c}\) is perpendicular to both \(\mathbf{a}\) and \(\mathbf{b}\), and \(\mathbf{a}\) is perpendicular to both \(\mathbf{b}\) and \(\mathbf{c}\).
  2. The magnitude of the cross product \(\mathbf{a} \times \mathbf{b}\) is given by: \(|\mathbf{a} \times \mathbf{b}| = ab\sin\theta = c\), where \(\theta\) is the angle between \(\mathbf{a}\) and \(\mathbf{b}\).
  3. Similarly, for \(\mathbf{b} \times \mathbf{c}\): \(|\mathbf{b} \times \mathbf{c}| = bc\sin\phi = a\), where \(\phi\) is the angle between \(\mathbf{b}\) and \(\mathbf{c}\).
  4. From the properties of cross product, since each pair of vectors forms a perpendicular set with the third vector, we also have the identity: \(a = b = c\) when considering they form an orthogonal unit vector system.
  5. By the nature of unit vectors specifically in orthogonal systems, and considering that all vectors have to satisfy the properties linked by cross products, \(\mathbf{b}\) must satisfy \(b = c\) to form a system without contradiction.
  6. Given the options and based on our analysis, the correct conclusion is:

\(a = 1, b = c\).

Therefore, the relationship between the magnitudes of the vectors \(\mathbf{a}\), \(\mathbf{b}\), and \(\mathbf{c}\) is such that \(a = 1\) and \(b = c\), which matches the correct answer provided.

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