For which value of kkk is the matrix A=(11k1k1k11)A = \begin{pmatrix} 1 & 1 & k \\ 1 & k & 1 \\ k & 1 & 1 \end{pmatrix}A=11k1k1k11 singular?
k=1k = 1k=1 or k=−2k = -2k=−2
k=0k = 0k=0
k=−1k = -1k=−1
k=2k = 2k=2