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GATE 2017 ME (ME1) – Question 11

Engineering Mathematics · Linear Algebra: Matrix algebra, systems of linear equations, eigen values and eigen vectors · 1 mark · Multiple choice

Find the product of the eigenvalues of $$P=\begin{pmatrix}2&0&1\\4&-3&3\\0&2&-1\end{pmatrix}.$$

  1. −6
  2. 2
  3. 6
  4. −2

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Correct answer: (B) 2

Explanation

The product of eigenvalues, with algebraic multiplicity, equals the determinant. Expanding along the first row gives $\det P=2[(-3)(-1)-3(2)]+1[4(2)-(-3)(0)]=2(3-6)+8=2$. Thus the required product is 2, B; solving the characteristic cubic is unnecessary.

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