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GATE 2024 ST – Question 13

Matrix Theory · Vector Spaces and Linear Systems · 1 mark · Multiple choice

For a real 3×3 A, which claim is not true?

  1. RREF(A)=I implies zero is not an eigenvalue.
  2. Zero not an eigenvalue implies RREF(A)=I.
  3. Three distinct eigenvalues imply RREF(A)=I.
  4. If Ax=b is solvable for every real b, RREF(A)=I.

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Show answer and explanation

Correct answer: (C) Three distinct eigenvalues imply RREF(A)=I.

Explanation

A,B,D are equivalent formulations of invertibility. Distinct eigenvalues do not exclude zero: diag(0,1,2) has three distinct eigenvalues but rank 2 and RREF different from I. Thus **C**.

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