For which kkk is the matrix (k101k101k)\begin{pmatrix} k & 1 & 0 \\ 1 & k & 1 \\ 0 & 1 & k \end{pmatrix}k101k101k singular?
k=0k = 0k=0
k=±2k = \pm \sqrt{2}k=±2
k=0,±2k = 0, \pm \sqrt{2}k=0,±2
k=1k = 1k=1