What Is the Value of k That Makes This Matrix Non-Invertible?

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The discussion centers on finding the value of k that makes the given matrix non-invertible. Participants express confusion over the correct value, with one asserting it should be k = 1 while others disagree, suggesting different values such as -3. There is a consensus that the matrix is singular, but discrepancies in calculations lead to uncertainty about the correct answer. Users are encouraged to recheck their work and ensure accuracy in their determinant calculations. The conversation highlights the importance of verifying mathematical results and the potential for errors in computation.
wayneo
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determine the value of k for which the matrix

(2 4 1)
(k -1 2)
(7 7 4) has no inverse

apparently the answer is k = 1 but I can't see how.

I worked it out to be -3
 
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Can you show your work?

I obtained an answer that isn't k=1, by the way. Are you sure you copied the matrix and/or the answer down correctly ?
 
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I agree that it is not one, but I don't agree with your answer of -3. Assuming that the matrix you gave is correct, look back at your working (preferably post what you have done) - I checked my result with my calculator, and found the matrix to be singular.
 
see I just wanted to be sure whether the book was wrong or not as it says it is 1. I tried working out the determinant step by step and making it equal to 0 then solve for 'k' like an algebra equation
 
I worked it out to be neither 1 nor -3, and double checked in matlab.

rework and check your signs carefully.
 

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