Suppose A and B are n × n matrices. Show that range(AB) ⊆ range(A)

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Homework Help Overview

The problem involves demonstrating that the range of the product of two n × n matrices, AB, is a subset of the range of matrix A. The subject area pertains to linear algebra and matrix theory.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the need to show that AB is a linear combination of the columns of A. Some express uncertainty about how to rigorously prove this statement for all n × n matrices. Others question the precise meaning of elements belonging to the range of AB.

Discussion Status

The discussion includes various perspectives on the problem, with some participants acknowledging the truth of the statement while struggling to articulate a formal proof. There is an ongoing exploration of definitions and assumptions related to the ranges of the matrices involved.

Contextual Notes

There is a mention of the original poster's username leading to a moderator action, which may affect the continuity of the discussion.

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Homework Statement



Suppose A and B are n × n matrices. Show that range(AB) ⊆ range(A)


Homework Equations





The Attempt at a Solution



I think I need to show AB is a linear combination of the columns of A, but I'm not sure how to show this in general.
 
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welcome to pf!

hi jazz_hole! welcome to pf! :smile:
jazz_hole said:
Suppose A and B are n × n matrices. Show that range(AB) ⊆ range(A)

isn't it obvious? :wink:
 
I can see how it is true, but I don't know how to show it rigorously. For all n x n matrices.
 
Assume ##y \in \text{range}(AB)##. Show that ##y \in \text{range}(A)##.

You need to understand what is meant precisely when you say ##y \in \text{range}(AB)##.
 
jazz_hole said:
I can see how it is true, but I don't know how to show it rigorously.

start "let y ε range (AB)

then there exists …" :wink:
 
Moderator note -- The OP has been banned because of his choice of username.
 

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