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GATE 2020 CH – Question 35

Engineering Mathematics · Linear Algebra: Matrix algebra, systems of linear equations, eigenvalues and eigenvectors · 1 mark · Numerical answer

Find the sum of eigenvalues of $$\begin{pmatrix}2&4&6\\3&5&9\\12&1&7\end{pmatrix},$$ rounded to the nearest integer.

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Correct answer: 14 to 14

Explanation

The sum of eigenvalues, counted with algebraic multiplicity, equals the matrix trace. Sum the diagonal entries: 2 + 5 + 7 = 14. This identity holds whether or not all eigenvalues are real and does not require solving the characteristic polynomial.

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