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GATE 2025 ST – Question 38

Matrix Theory · Eigenvalues and Matrix Decompositions · 2 marks · Multiple choice

A 10×10 real P has diagonal entries 9/10 and off-diagonal entries −1/10. Find its rank.

  1. 10
  2. 9
  3. 1
  4. 8

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Correct answer: (B) 9

Explanation

P=I−J/10, where J is the all-ones matrix. It annihilates the all-ones vector and is the identity on its nine-dimensional orthogonal complement. Eigenvalues are 0 once,1 nine times, so **rank=9, B**.

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