Linear Algebra Inverse Generalization

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Homework Help Overview

The discussion revolves around a linear algebra problem involving the properties of a square matrix \( T \) where \( T^4 \) is the zero matrix. The original poster seeks to show that \( (I-T)^{-1} = I+T+T^2+T^3 \) and to generalize this result.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the multiplication of \( (I+T+T^2+T^3)(I-T) \) to verify if it results in the identity matrix. There is a suggestion to confirm this through matrix operations, and some participants express uncertainty about the implications of the calculations.

Discussion Status

The discussion is active, with participants engaging in verification of the mathematical expression and exploring the conditions under which the generalization holds. There is a light-hearted exchange about the nature of linear algebra, but the focus remains on confirming the algebraic manipulation.

Contextual Notes

Participants note that \( T^4 = 0 \) is a critical assumption for the problem, and there is an emphasis on the need for generalization beyond the specific case presented.

gabriels-horn
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Homework Statement


Show that if [tex]T[/tex] is a square (matrix) and if [tex]T^4[/tex] is the zero matrix then [tex](I-T)^{-1} = I+T+T^2+T^3[/tex]. Generalize.

The Attempt at a Solution


To be honest I don't even know where to begin. Supposedly this is a simple generalization.
 
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Well, what is [itex](I+T+T^2+T^3)(I-T)[/itex]?
 
gabbagabbahey said:
Well, what is [itex](I+T+T^2+T^3)(I-T)[/itex]?

Is it...[tex]I[/tex]?
 
confirm it by multplying out. matrix addition & multiplication are distrubutive.
 
lanedance said:
confirm it by multplying out. matrix addition & multiplication are distrubutive.

Yeah, I know. It was a joke; of course its I. Everything in Linear is I.
 
gabriels-horn said:
Is it...[tex]I[/tex]?

Multiplying it out should give you [itex]I-T^4[/itex]. So, if [itex]T^4=0[/itex],, then you get the identity matrix and hence [itex](1+T+T^2+T^3+T^4)=(I-T)^{-1}[/itex].

Now, can you generalize this statement?
 

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