Matrix manipulation (inverse, lin. alg.)

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Homework Help Overview

The discussion revolves around a linear algebra problem involving matrix manipulation, specifically focusing on the properties of a matrix \( A \) that satisfies the equation \( A^{3}-A^{2}-I_{n}=0 \). Participants are tasked with demonstrating the invertibility of \( A \) and exploring the uniqueness of solutions to a related equation.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants express confusion regarding the initial steps to demonstrate the invertibility of the matrix and the implications of the given equation. Some participants attempt to manipulate the equation algebraically to show that \( A \) is invertible, while others share their interpretations of the problem and seek clarification on specific steps.

Discussion Status

The discussion is ongoing, with some participants providing algebraic insights and others requesting further assistance with the final steps of the solution. There is a mix of understanding and uncertainty, indicating that while some progress has been made, additional guidance is still sought.

Contextual Notes

Participants mention the pressure of upcoming exams, which may influence their approach to the problem. There is also a recognition of the simplicity of the algebra involved, contrasting with the participants' initial apprehensions about matrix manipulations.

boings
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Homework Statement



Let A\inM_{n}(\Re) a matrix verifying

A^{3}-A^{2}-I_{n}=0

a) Show that A is inversible and calculate it
b) Show that the solution X\subsetM_{n}(\Re) of the equation

A^{k}(A-I_{n})X=I_{n}

has a unique solution.





The Attempt at a Solution



I'm having trouble with starting this one. I'm quite rubbish with these matrices in linear algebra, but I have exams in a few days and this question was on it, so i need help!

I know the criteria for matrix inverse (AB=BA=I). However there's too much going on... help me dissect it? thanks a lot to anyone for any help, much appreciated.
 
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boings said:

Homework Statement



Let A\inM_{n}(\Re) a matrix verifying

A^{3}-A^{2}-I_{n}=0

a) Show that A is inversible and calculate it
This is kind of trivial! A^3- A^2= A(A^2- A)= (A^2- A)A= I.

b) Show that the solution X\subsetM_{n}(\Re) of the equation

A^{k}(A-I_{n})X=I_{n}

has a unique solution.
Again, from A^3- A^2- I= 0, we have A^2(A- I)= I so for any k\ge 2, A^k(I- I)X= A^{k-2}(A^2(A- I)X= A^{k- 2}X= I. And since A has an inverse, you just multiply both sides by A^{-1} k- 2 times. The cases where k= 0 or k= 1 are simple.

The Attempt at a Solution



I'm having trouble with starting this one. I'm quite rubbish with these matrices in linear algebra, but I have exams in a few days and this question was on it, so i need help!

I know the criteria for matrix inverse (AB=BA=I). However there's too much going on... help me dissect it? thanks a lot to anyone for any help, much appreciated.

There was really no "matrix" algebra involved here, just the definitions and basic algebraic manipulation.
 
Oh I see, that was easier than I thought. I always get tripped up when they mention matrices and think that I have to tread very cautiously.

thank you
 
Actually, can you help me out with the last steps for solving? I'm still a bit caught up. I attached my attempt where you left off.

thanks
 

Attachments

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