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GATE 2020 AG – Question 12

Engineering Mathematics · Linear Algebra · 1 mark · Multiple choice

A linear system has n unknowns. Its coefficient and augmented matrices have ranks r₁ and r₂. Which condition ensures a unique consistent solution?

  1. r₁≠r₂<n
  2. r₁=r₂=n
  3. r₁=r₂<n
  4. r₁≠r₂>n

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Show answer and explanation

Correct answer: (B) r₁=r₂=n

Explanation

Consistency requires the two ranks to agree. Uniqueness additionally requires rank n, leaving no free variables. Thus r₁=r₂=n, B. Equal ranks below n give infinitely many solutions, whereas unequal ranks make the system inconsistent.

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