For what value of kkk does the matrix A=[123−2−4k36−9]A = \begin{bmatrix} 1 & 2 & 3 \\ -2 & -4 & k \\ 3 & 6 & -9 \end{bmatrix}A=1−232−463k−9 have rank 2?
k=0k = 0k=0
k=−6k = -6k=−6
k=6k = 6k=6
k=9k = 9k=9