Determinant Expansions: Intuitive Understanding & Proofs

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SUMMARY

The discussion centers on the concept of determinant expansions in linear algebra, specifically addressing why the value of a determinant remains invariant regardless of the row or column chosen for expansion. Participants emphasize that the determinant reflects properties of the linear transformation represented by the matrix rather than the matrix itself. A key insight shared is that a basis transformation can be employed to demonstrate this invariance, allowing for any row or column to be treated as the first in the expansion process.

PREREQUISITES
  • Understanding of linear transformations and their representation via matrices.
  • Familiarity with the concept of determinants in linear algebra.
  • Knowledge of basis transformations and their implications in vector spaces.
  • Basic proof techniques in mathematics, particularly in the context of linear algebra.
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  • Study the geometric interpretation of determinants in linear transformations.
  • Learn about basis transformations and their effects on matrix representations.
  • Explore detailed proofs of determinant properties, focusing on expansion methods.
  • Investigate applications of determinants in solving systems of linear equations.
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Students of linear algebra, educators seeking intuitive explanations of determinants, and mathematicians interested in the foundational properties of matrix transformations.

heshbon
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Hi, I can't understand why any determinant expansion is the same via any row/column.
My lecturer says the proof is too technical to go over,
Does anyone have a good way to think about it intuitavely or know a site which has a full proof?
thnx
 
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This is a bit of a vague argument, but I think it is the underlying thought:
The determinant is not so much a property of a matrix, but actually a property of the map which that matrix represents (and usually as such can be assigned a geometric meaning). Therefore, it should not depend on details like which basis we happen to write the matrix in.

I'm not sure we can offer you much rigor without actually going into the proof :smile:

I think the proof is here by the way, at least for expansion along the first row and column. You can just do a basis transformation (permute the basis vectors) to get any row/column you want as the first one.
 
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