Are These Linear Algebra Statements True or False?

  • Context: Undergrad 
  • Thread starter Thread starter ammar555
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around the truth of specific statements related to linear algebra, particularly concerning subsets of vector spaces and their properties. Participants explore counterexamples and seek clarification on the implications of these statements.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification
  • Homework-related

Main Points Raised

  • Some participants assert that two subsets of a vector space that span the same subspace do not have to be equal, providing examples such as the subsets {1} and {-1} generating the real line R.
  • Others argue that the union of two subspaces does not necessarily form a subspace, using the example of the x and y axes in R², where the addition of vectors from these axes results in a vector outside both subspaces.
  • A participant expresses uncertainty about the implications of the examples provided and questions whether their understanding of the second statement is incorrect.
  • Further clarification is offered regarding the distinction between addition and set union of vector subspaces, emphasizing that they are not equivalent operations.
  • Some participants suggest that additional reading on vector spaces may help clarify the concepts discussed.

Areas of Agreement / Disagreement

Participants generally agree on the falsehood of the statements in question, but there remains uncertainty regarding the implications and understanding of the examples provided, particularly for the second statement.

Contextual Notes

Participants express varying levels of understanding and seek further clarification on the concepts, indicating that some assumptions or definitions may not be fully articulated in the discussion.

ammar555
Messages
12
Reaction score
0
I have these questions on my studyguide and I know both of them are false. I just don't have a good counterexample or a good explaintion to prove so.

1) two subsets of a vector space V that span the same subspace of V are equal.

False: They don't have to be equal

2) The union of any 2 subspaces of a vector space V is a subspace of V.

False: Adding two subspaces doesn't necessary mean they will stay inside the vector space
 
Physics news on Phys.org
1) +1 and -1 in R
2) x and y axes in R^2. Addition and set union of two vector subspaces are not equal notions, though.
 
Alesak said:
1) +1 and -1 in R
2) x and y axes in R^2. Addition and set union of two vector subspaces are not equal notions, though.

Please I need a little more explaintions, I don't fully understand your examples. And does that mean my answer to number 2 is wrong?

Thanks though!
 
1) real line R is a vector space, and it is generated by both +1 and -1. So these two one-element subsets {1} and {-1} generate R yet are different.

2) it's correct, just unclear. Consider, for example, subspaces of R^2 that coincide with usual x and y axes. Vector (1, 0) is on x axis, vector (0, 1) on y axis, but if you add them they lie out of both subspaces.

So set theoretic union of two vector subspaces doesn't have to be vector subspace. Perhaps you can try to work out operation that makes some kind of "union" of two vector subspaces again a subspace.

You can surely find more information about vector spaces on wikipedia or in your textbook.
 
Alesak said:
1) real line R is a vector space, and it is generated by both +1 and -1. So these two one-element subsets {1} and {-1} generate R yet are different.

2) it's correct, just unclear. Consider, for example, subspaces of R^2 that coincide with usual x and y axes. Vector (1, 0) is on x axis, vector (0, 1) on y axis, but if you add them they lie out of both subspaces.

So set theoretic union of two vector subspaces doesn't have to be vector subspace. Perhaps you can try to work out operation that makes some kind of "union" of two vector subspaces again a subspace.

You can surely find more information about vector spaces on wikipedia or in your textbook.


Much better explanations precisely for number 1, I think I understand it now. Number 2 I'm still shady about it. Maybe if I read more about vectors, I can then understand it more clearly.

Thanks a million times!
 
ammar555 said:
Much better explanations precisely for number 1, I think I understand it now. Number 2 I'm still shady about it. Maybe if I read more about vectors, I can then understand it more clearly.

Thanks a million times!

Sure, get any good textbook on linear algebra, it will be crystal clear to you in no time.
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 6 ·
Replies
6
Views
4K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 1 ·
Replies
1
Views
2K