Is Span{u1,u2,...,um} a Subspace of R^n?

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    Proof Span Subspace
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Discussion Overview

The discussion revolves around the question of whether the span of a set of vectors {u1, u2, ..., um} in R^n is a subspace of R^n. Participants explore definitions and properties related to spans and subspaces, seeking to clarify the requirements for proving the assertion directly.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant requests guidance on how to begin proving that the span is a subspace.
  • Another participant suggests that the definition of span as the smallest subspace containing the vectors makes the result trivial.
  • It is noted that span can be defined as the set of all linear combinations of the vectors, which is a subset of the vector space.
  • A participant questions the distinction between a subspace and a subset, prompting a discussion about the properties that define a subspace.

Areas of Agreement / Disagreement

Participants express differing views on the definitions of span and subspace, and there is no consensus on how to approach the proof directly.

Contextual Notes

The discussion highlights the need for clarity on definitions and properties related to spans and subspaces, but does not resolve these issues.

Who May Find This Useful

This discussion may be useful for students learning about vector spaces, spans, and subspace properties in linear algebra.

squenshl
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I have a problem.
Suppose that {u1,u1,...,um} are vectors in R^n. Prove, dircetly that span{u1,u2,...,um} is a subspace of R^n.
How would I go by doing this?
 
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Well, directly, as the question asks. Where are you stuck?
 
Depends on your definition of span (my favourite being span {u1, ..., um} = the smallest subspace containing u1, ..., um, from which the result is trivial). ;)

You probably define span {u1, ..., um} = {a1u1 + ... + amum | a1, ..., am in R}. Just apply your definition of (or test for) a subspace.
 
I just need to know how to get started.
 
squenshl said:
I just need to know how to get started.

Well, your span (probably meaning as adriank pointed out) is the the set of all linear combinations of those vectors. So that's clearly a subset of your vector space, right?

So, what's the difference between a subspace of a vector space and just a plain old subset? What's the magic property that spaces have that sets don't? Then you just need to demonstrate that your subset has it.
 

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