For the system {2x+y=54x+ky=10\begin{cases} 2x + y = 5 \\ 4x + ky = 10 \end{cases}{2x+y=54x+ky=10, Cramer's rule cannot be applied when:
k=1k = 1k=1
k=2k = 2k=2
k=4k = 4k=4
k=5k = 5k=5