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GATE 2021 MA – Question 59

Linear Algebra · Eigenvalues and Canonical Forms · 2 marks · MTA

A has characteristic polynomial det(xI−A)=x⁴(x−1)²(x−2)³. If rank(A²)<rank(A³)=rank(A⁴), find the geometric multiplicity of eigenvalue zero.

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Correct answer: MTA

Explanation

The official grading is **marks to all**. For every matrix, range(A³)⊆range(A²), so rank(A³)≤rank(A²). The printed strict inequality reverses this unavoidable monotonicity, and no matrix can satisfy the premises. The geometric multiplicity therefore cannot be inferred from a consistent example. The invalid premise is retained and explained.

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