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GATE 2021 MA – Question 11

Linear Algebra · Vector Spaces and Linear Transformations · 1 mark · Multiple choice

A is real 3×4 and B real 4×3, with AB nonsingular. P:nullity A=0. Q:BA is nonsingular. Choose truth values.

  1. Both P and Q true
  2. P true, Q false
  3. P false, Q true
  4. Both false

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Show answer and explanation

Correct answer: (D) Both false

Explanation

AB has rank 3, forcing rank A=rank B=3. Since A has four columns, nullity A=4−3=1, so P fails. The 4×4 product BA has rank at most 3 and is singular, so Q fails. **D**.

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