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GATE 2023 ST – Question 36

Matrix Theory · Inner Products and Quadratic Forms · 2 marks · Multiple choice

For a real n×n matrix A: I:if A is symmetric,there exists c≥0 for which A+cI is symmetric positive definite. II:if A is symmetric positive definite,there exists symmetric positive definite B with A=B². Which hold?

  1. Only I
  2. Only II
  3. Both I and II
  4. Neither I nor II

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Correct answer: (C) Both I and II

Explanation

A symmetric matrix has real eigenvalues. Choose c>max(0,−λ_min) to make all shifted eigenvalues positive,proving I. For II,spectral decomposition A=Q diag(λ_i)Qᵀ with λ_i>0 gives B=Q diag(√λ_i)Qᵀ. Both hold. **C**.

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