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GATE 2026 MA – Question 57

Linear Algebra · Inner Products and Quadratic Forms · 2 marks · Numerical answer

Maximize $z=x^T\begin{pmatrix}2&0&0\\0&2&1\\0&1&2\end{pmatrix}x$ over real vectors with xᵀx=1. Find the maximum (integer).

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Correct answer: 3 to 3

Explanation

For a real symmetric matrix the maximum Rayleigh quotient is its largest eigenvalue. Eigenvalues are 2 from the first coordinate and 2±1 = 3,1 from the lower block. Maximum is **3**, attained by x=(0,1/√2,1/√2)ᵀ.

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