Q. The Eigen values of the matrix $\begin{bmatrix}x-a & 0 & 0 \\ x-b & x-c & 0 \\ x-d & x-e & x-f\end{bmatrix}$ are equal $\forall x$, then

Solution:

Since the matrix is triangular the diagonal elements are the Eigen values.
By the given condition, $x-a=x-c=x-f $
$ \therefore a=c=f$.