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GATE 2026 BM – Question 18

Engineering Mathematics · Linear Algebra · 1 mark · Multiple choice

Invertible n×n matrix P satisfies P³=I. Which must hold?

  1. P⁵=P
  2. P⁵=P⁻¹
  3. P⁴=P⁻¹
  4. P⁴=P²

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Show answer and explanation

Correct answer: (B) P⁵=P⁻¹

Explanation

From P³=I, multiplying by P⁻¹ gives P²=P⁻¹. Also P⁵=P³P²=P². Combining them yields P⁵=P⁻¹, B. The other equalities require extra restrictions on P and are not universal.

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