Linear Algebra Proof: Prove r(CA) < n

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SUMMARY

The discussion centers on proving that if A is an n x n matrix with rank(A) < n, then for any n x n matrix C, the rank of the product CA, denoted as r(CA), is also less than n. The participants emphasize the importance of understanding the properties of matrix ranks and suggest referencing the Fundamental Theorem of Invertible Matrices to aid in the proof. The discussion highlights that the dimensions of the row and column spaces of matrix A are critical in establishing the relationship between the ranks of A and CA.

PREREQUISITES
  • Understanding of matrix rank and its implications
  • Familiarity with the Fundamental Theorem of Invertible Matrices
  • Knowledge of linear transformations and their properties
  • Basic concepts of matrix multiplication
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  • Study the Fundamental Theorem of Invertible Matrices in detail
  • Explore the implications of rank-nullity theorem
  • Learn about properties of linear transformations and their effects on rank
  • Investigate examples of matrix products and their ranks
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Students and educators in linear algebra, mathematicians focusing on matrix theory, and anyone seeking to deepen their understanding of matrix ranks and their properties.

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Homework Statement



Prove (without using determinants):

If A is an n x n matrix and r(A) < n, then for any n x n matrix C, r(CA) < n.
Hint: Can CA be invertible?

2. The attempt at a solution

Well, I'm running on almost very little sleep, so I can't really think today. What's the proof?

And...i spelled algebra wrong...
 
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I'm assuming that r(A) stands for rank(A), if so, then we have that the dimension of the row and column spaces are smaller than n. I'm not going to do the work for you, but take a look at the Fundamental Theorem of Invertible matrices, there's something in there that will greatly help you (One of the properties).

Try to show some work though.
 

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