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GATE 2020 ST – Question 9

General Aptitude · Quantitative Aptitude: Algebra, Geometry and Mensuration · 2 marks · Multiple choice

A4×4 matrix has zero diagonal and mij=−mji. How many independent elements fully specify it?

  1. 0
  2. 6
  3. 12
  4. 16

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Show answer and explanation

Correct answer: (B) 6

Explanation

Skew symmetry determines every below-diagonal entry from its above-diagonal partner. The diagonal is already fixed at zero. Therefore choose the4×3/2=6 entries above the diagonal, B; their six negatives complete the matrix.

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