Linear Algebra: Vector space axioms

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Homework Help Overview

The discussion revolves around the axioms of vector spaces, specifically evaluating whether a given set of polynomials of degree three or higher, including zero, qualifies as a vector space. The original poster questions the validity of the axiom 1*x = x in this context.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the implications of the vector space axioms, particularly focusing on closure under vector addition and the existence of a zero vector. Questions arise regarding the original poster's understanding of the axioms and the specific properties of the polynomial set.

Discussion Status

The discussion is active, with participants providing insights into the requirements for a vector space. Some guidance has been offered regarding the importance of closure under addition and the necessity of a zero vector, although there is no explicit consensus on the original poster's understanding of the axioms.

Contextual Notes

There is a mention of the original post asserting that zero is included in the set, which raises further questions about the implications for vector addition and the overall structure of the space.

preet
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Homework Statement


One of the fundamental axioms that must hold true for a set of elements to be considered a vector space is as follows:
1*x = x

I was given a particular space: The set of all polynomials of degree greater than or equal to three, and zero, and asked to evaluate whether or not it was a vector space or not. The one that doesn't hold true is 1*x=x (according to the solutions), but I don't understand why. I can't find a situation where the above axiom holds true. Could anyone help me out?

Thanks
Preet
 
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I'd check the solutions again. The problem is closure under vector addition.
 
The set of vectors and the vector addition must form an abelian group. That is true for those polynomials. However, your polynomial space lacks the "null/zero vector"; since we know that the scalar zero times any vector from your set should give the zero vector. Since the zero vector is not an element of the space, it follows that the polynomials' space plus vector addition plus scalar multiplication do not yield a vector space.

Daniel.
 
Daniel, the original post says that zero is an element of the set. The problem is indeed vector addition, since [itex]x^3 + (-x^3 + 1) = 1[/itex], for exampl.
 

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