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

  • Thread starter Thread starter wayneo
  • Start date Start date
  • Tags Tags
    Homework Matrices
Click For Summary

Homework Help Overview

The discussion revolves around determining the value of k that makes a given 3x3 matrix non-invertible by analyzing its determinant. Participants are exploring the implications of this condition in the context of linear algebra.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants are attempting to calculate the determinant of the matrix and set it to zero to find the value of k. There are questions about the correctness of the matrix representation and the answers obtained.

Discussion Status

The discussion is ongoing, with several participants expressing differing results and questioning each other's calculations. Some have suggested re-evaluating the determinant and checking for potential errors in signs or assumptions.

Contextual Notes

There is a reference to a textbook answer that states k=1, which some participants are questioning. The accuracy of the matrix provided and the calculations performed is under scrutiny.

wayneo
Messages
31
Reaction score
0
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
 
Physics news on Phys.org
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 ?
 
Last edited:
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.
 

Similar threads

Replies
6
Views
2K
  • · Replies 69 ·
3
Replies
69
Views
11K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
Replies
24
Views
4K
  • · Replies 22 ·
Replies
22
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K