If A=(k00k)A = \begin{pmatrix} k & 0 \\ 0 & k \end{pmatrix}A=(k00k), for what kkk is det(A)=9\det(A) = 9det(A)=9?
k=3k = 3k=3
k=9k = 9k=9
k=±3k = \pm 3k=±3
k=±9k = \pm 9k=±9