Linear Algebra - Proof of the characteristic polynomial for the inverse of A

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SUMMARY

The discussion focuses on proving the characteristic polynomial for the inverse of an invertible matrix A, specifically showing that PA-1(x) = (-x)n/det(A) * PA(1/X). The key equation utilized is det(AB) = det(A)det(B), which is essential for manipulating the determinant expressions. Participants highlight the importance of substituting the definition of the characteristic polynomial, det(A - λI) = 0, into the proof to derive the desired result through matrix arithmetic.

PREREQUISITES
  • Understanding of characteristic polynomials in linear algebra
  • Familiarity with matrix determinants and properties
  • Knowledge of invertible matrices and their characteristics
  • Basic skills in matrix arithmetic and manipulation
NEXT STEPS
  • Study the derivation of characteristic polynomials for various matrix types
  • Learn about the implications of matrix invertibility on determinants
  • Explore advanced topics in linear algebra, such as eigenvalues and eigenvectors
  • Investigate applications of characteristic polynomials in systems of linear equations
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Students of linear algebra, mathematicians, and educators seeking to deepen their understanding of matrix theory and characteristic polynomials.

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Homework Statement



A is an nxn invertible matrix. Show that

PA-1(x) = (\frac{(-x)^n}{det(A)}) *PA(1/X)

Homework Equations


det(AB) = det(A)det(B)


The Attempt at a Solution



Ok from what I understand this is the proof for the characteristic polynomial for the inverse of a matrix. The professor said that we need to use somehow the equation above.

I also understand that the equation is usually of the form det(A-\lambdaI) = 0, but I cannot see how to form this given the final equation which we need to produce.
 
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Try substituting the definition of the characteristic polynomial into the equation you are trying to verify. You get \det(Ix- A^{-1}) = \frac{(-x)^n\det(Ix^{-1} - A)}{\det(A)} If you notice that \det(-Ix) = (-x)^n, then the rest is matrix arithmetic using the equation you provided.

Good luck!
 

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