Question:
The system of equations $\mathrm{kx}+\mathrm{y}+\mathrm{z}=1, \mathrm{x}+\mathrm{ky}+\mathrm{z}=\mathrm{k}$ and $\mathrm{x}+\mathrm{y}+\mathrm{z} \mathrm{k}=\mathrm{k}^{2}$ has no solution if $\mathrm{k}$ is equal to :
Correct Option: , 4
Solution:
$\mathrm{kx}+\mathrm{y}+\mathrm{z}=1$
$x+k y+z=k$
$x+y+z k=k^{2}$
$\Delta=\left|\begin{array}{ccc}\mathrm{K} & 1 & 1 \\ 1 & \mathrm{~K} & 1 \\ 1 & 1 & \mathrm{~K}\end{array}\right|=\mathrm{K}\left(\mathrm{K}^{2}-1\right)-1(\mathrm{~K}-1)+1(1-\mathrm{K})$
$=K^{3}-K-K+1+1-K$
$=K^{3}-3 K+2$
$=(K-1)^{2}(K+2)$
For $\mathrm{K}=1$
$\Delta=\Delta_{1}=\Delta_{2}=\Delta_{3}=0$
But for $\mathrm{K}=-2$, at least one out of $\Delta_{1}, \Delta_{2}, \Delta_{3}$
are not zero
Hence for no soln, $K=-2$