Finding the Span of u1 & u2 in R^3

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Discussion Overview

The discussion revolves around describing the span of two vectors, u1 and u2, in R^3. Participants explore the implications of the vectors' components and seek to understand the geometric representation of their span.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant expresses uncertainty about how to proceed after determining the span as a linear combination of u1 and u2, represented as (a+b, a-b, a+b).
  • Another participant suggests using Gaussian elimination or considering vectors perpendicular to u1 and u2 to gain further insight.
  • A repeated post reiterates the initial problem and introduces specific combinations of u1 and u2, leading to vectors (0, 1, 0) and (1, 0, 1), which may clarify the span's characteristics.
  • One participant questions whether the span corresponds to the x-z plane in R^3.
  • Another participant points out that the first and third components of the vectors are equal, prompting a discussion about the implications for characterizing the vectors.
  • A participant suggests that the equation x=z describes all vectors in the span.

Areas of Agreement / Disagreement

The discussion contains multiple viewpoints regarding the geometric interpretation of the span, with some participants proposing different characterizations and equations without reaching a consensus.

Contextual Notes

Participants have not fully resolved the implications of the vectors' components or the specific nature of the span, leaving some assumptions and definitions unaddressed.

physicsss
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I'm stuck on the following problem:

Describe the span of the vectors u1 and u2 in R^3, where
u1 = (1, 1, 1), u2 = (1, −1, 1)

I know that the span is a(u1)+b(u2), which becomes (a+b,a-b,a+b), but I don't know where to go from here.

TIA.
 
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do you know gaussian elimination, reduction for matrices?

i.e. how to solve for all vectors perpendicular to both of those?

or you could just look at your general vector, since it satisfies an obvious equation.
 
physicsss said:
I'm stuck on the following problem:

Describe the span of the vectors u1 and u2 in R^3, where
u1 = (1, 1, 1), u2 = (1, −1, 1)

I know that the span is a(u1)+b(u2), which becomes (a+b,a-b,a+b), but I don't know where to go from here.

TIA.
Consider (1/2)(u1-u2)=(0,1,0) and (1/2)(u1+u2)=(1,0,1)
It will then be easier to see what is happening.
 
Is it the x-z plane in R^3?
 
have you noticed that the first and third entries of your vectors are equal? what does that tell you about an equations characterizing these vectors?
 
The main diagonal line in x-z plane
 
i.e. x=z describes all of these vectors.
 

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