Solve Unknown b in Matrix C for No Unique Solutions

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Discussion Overview

The discussion revolves around determining the values of b in a given matrix C such that the system of equations y = Cx does not have a unique solution. The focus is on the relationship between the determinant, rank of the matrix, and the conditions for non-unique solutions.

Discussion Character

  • Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant seeks assistance in finding values of b that lead to no unique solutions for the system y = Cx.
  • Another participant questions the relationship between the system determinant and the uniqueness of the solution.
  • A different participant expresses uncertainty about the determinant's role, suggesting it may relate to basis interdependency rather than uniqueness.
  • One participant notes that for a unique solution, the rank of matrix A must equal n, but they are unsure how to determine the rank.
  • Another participant points out that if b = 3, the fourth column of matrix C becomes a multiple of the first column, leading to a rank less than n and thus resulting in no unique solutions.
  • A later reply acknowledges the previous point, indicating understanding of the relationship between b and the uniqueness of solutions.

Areas of Agreement / Disagreement

Participants express differing views on the role of the determinant and rank in determining the uniqueness of solutions. Some agree on the implications of b = 3, while others remain uncertain about the broader principles involved.

Contextual Notes

Participants have not fully resolved the relationship between the determinant and the uniqueness of solutions, nor have they established a clear method for determining the rank of the matrix.

blackbear
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I have the following matrix C =

3 2 1 9
4 2 6 12
1 4 -3 3
0 1 8 (3-b)

y1=[-1 -1 1 -1] transpose

For the vector y, I need to find all values of b such that the system of equations y=Cx has no unique solutions. Can someone help...

Thanks
 
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What is the relation between the system determinant and the uniqueness of the solution?
 
I am not sure...I thought the system determinant is only used to find the interdependency of the basis. If there exist such a relation as you have mentioned...that is not mentioned in the question; so we can assume anything for the problem.
 
By the way in order to have a unique solution r(A), rank equals n. But we know n but I don't know how to get rank!
 
Notice how if b = 3 then column 4 becomes a multible of column 1. This solution would make the rank(C) < n = 4 and therefore C would not have an inverse making the system have no unique solitions.
 
Thanks Live2Learn...I got it!
 

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