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GATE 2020 IN – Question 36

Engineering Mathematics · Linear algebra and matrices: Matrix algebra, systems of linear equations, consistency and rank, eigenvalues and eigenvectors, tensors · 2 marks · Multiple choice

For $$M=\begin{pmatrix}1&-1&0\\1&-2&1\\0&-1&1\end{pmatrix},$$ which is an eigenvector?

  1. $$\begin{pmatrix}1\\-1\\1\end{pmatrix}$$
  2. $$\begin{pmatrix}1\\1\\-1\end{pmatrix}$$
  3. $$\begin{pmatrix}-1\\1\\-1\end{pmatrix}$$
  4. $$\begin{pmatrix}1\\1\\1\end{pmatrix}$$

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Correct answer: (D) $$\begin{pmatrix}1\\1\\1\end{pmatrix}$$

Explanation

An eigenvector is nonzero and satisfies $Mv=\lambda v$. For $v=(1,1,1)^T$, multiplication gives $(0,0,0)^T$, so it is an eigenvector with eigenvalue 0. The other displayed vectors do not produce scalar multiples of themselves. Hence D.

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