SOLUTION: Determine the values of k such that the system of linear equations does not have a unique solution. (Enter your answers as a comma-separated list.) x + y + kz = 4 x + k

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Question 1122187: Determine the values of k such that the system of linear equations does not have a unique solution. (Enter your answers as a comma-separated list.)
x + y + kz = 4
x + ky + z = 8
kx + y + z = 3

Answer by ikleyn(52858) About Me  (Show Source):
You can put this solution on YOUR website!
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The given system of equation does not have a unique solution if and only if the determinant of the coefficient matrix is equal to zero.


The determinant is equal to  -k%5E3+%2B+3k+-+2.


So, the condition under the question is satisfied if and only if 


    k%5E3+-+3k+%2B+2 = 0.


This polynomial has the roots  k= 1  (of the multiplicity 2)  and k= -2.


You can check on your own that the polynomial can be factored in this way


    k%5E3+-+3k+%2B+2 = %28k-1%29%5E2%2A%28k%2B2%29.


Answer.  The given system of linear equations does not have a unique solution if and only if  k= 1  and/or  k= -2.

Solved.

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On calculating the determinant of a 3x3-matrix see the lesson
    - Determinant of a 3x3 matrix
in this site.