The GATE Grind

GATE 2020 AE – Question 29

Engineering Mathematics · Linear Algebra: Vector algebra, matrix algebra, systems of linear equations, rank, eigenvalues and eigenvectors · 1 mark · Multiple choice

Find the sum of squared eigenvalues of $$A=\begin{pmatrix}\sin\theta&\tan\theta\\0&\cos\theta\end{pmatrix}.$$

  1. $\tan^2\theta$
  2. $1$
  3. $\sin^2\theta$
  4. $\cos^2\theta$

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (B) $1$

Explanation

An upper-triangular matrix has its diagonal entries as eigenvalues. Thus the sum of their squares is $\sin^2\theta+\cos^2\theta=1$, B, for θ where the matrix is defined. The off-diagonal tangent does not change these eigenvalues.

More Linear Algebra: Vector algebra, matrix algebra, systems of linear equations, rank, eigenvalues and eigenvectors questions

All Linear Algebra: Vector algebra, matrix algebra, systems of linear equations, rank, eigenvalues and eigenvectors questions →