Linear Algebra: Show it's a vector space question

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Homework Help Overview

The problem involves defining a set V = R with a non-standard vector addition defined as a + b = ab and scalar multiplication as za = a^z. The task is to demonstrate that V satisfies the properties of a vector space.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the verification of vector space axioms, particularly focusing on the additive identity and additive inverse. There is debate over the nature of the additive identity and whether it can be a single number applicable to all elements in V.

Discussion Status

The discussion is ongoing, with participants exploring the implications of the definitions provided. Some have suggested that the additive identity cannot depend on the specific element of V, while others question the existence of an additive inverse for certain elements, particularly zero. There is no explicit consensus on whether V can be classified as a vector space under the given definitions.

Contextual Notes

Participants note potential constraints regarding the definition of the additive identity and inverse, as well as the implications of including zero in the set V. There is also mention of the possibility of restricting V to positive real numbers to satisfy vector space properties.

jack_bauer
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Homework Statement



Define V =R with vector addition a+b=ab and scalar multiplication za=a^z.
Show that V is a vector space.




Homework Equations


a+b=ab, za=a^z


The Attempt at a Solution



I was able to check all the axioms but one, the additive inverse axiom where for all v in V there exists a... -v in V such that v+(-v)= 0. So far I have this: a+0=a(0)=0. In this case I believe 0 is the additive inverse.
 
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a(0) = 0 =/= a. So 0 is not the additive identity.

For the purposes of this thread, I propose using + and * to represent the addition and multiplication in the vector space (as opposed to canonical addition and multiplication in R) in order to avoid confusion
 
jack_bauer said:

Homework Statement



Define V =R with vector addition a+b=ab and scalar multiplication za=a^z.
Show that V is a vector space.




Homework Equations


a+b=ab, za=a^z


The Attempt at a Solution



I was able to check all the axioms but one, the additive inverse axiom where for all v in V there exists a... -v in V such that v+(-v)= 0. So far I have this: a+0=a(0)=0. In this case I believe 0 is the additive inverse.
While there is a single additive identity (and it is NOT 0), each member of V has a different additive inverse. The definition of "additive identity" (I will call it "O" for the moment) is that "a+ O= a". Here, "addition" of vectors is defined as the product of the numbers: "a+ b= ab" above. Therefore, "a+ O"= aO= a. What number is O?

However, I see a distince problem with this as stated. What is the additive inverse of the number 0? Also, if scalar multiplication is defined by za= az, what is (1/2)(-4)? Are you sure you were not supposed to take V= R+, the set of positive real numbers?
 
yeah I'm sure. would I be able to use 1/a for O then?
 
No, of course, not! There must be a single number, O, such that a"+" O= a. The additive identity cannot depend on what a is. Here, "+" is defined as "times: a"+" O= aO= a so O= 1. In that case, the additive inverse, "-a", must be such that a"+" ("-a")= O which now is interpreted as a("-a")= 1 or "-a"= 1/a. As I said in my first response, "While there is a single additive identity (and it is NOT 0), each member of V has a different additive inverse". The additive inverse of a is 1/a. That does NOT exist for a= 0 so this does NOT define a vector space.

If you restrict the set of vectors to the positive numbers only, then you have a vector space.
 

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