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GATE 2021 CS (CS2) – Question 47

Engineering Mathematics · Linear Algebra · 2 marks · Multiple choice

Define $s(P,Q)=\sum_{i=1}^nP[i]Q[i]$. A set L of nonzero ten-dimensional real vectors satisfies s(P,Q)=0 for every distinct pair. Find the maximum |L|.

  1. 9
  2. 10
  3. 11
  4. 100

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Correct answer: (B) 10

Explanation

Nonzero pairwise orthogonal vectors are linearly independent: taking the inner product of a linear dependence with each vector forces its coefficient to zero. There can be at most ten independent vectors in ten dimensions. The ten coordinate basis vectors attain the bound, so B.

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