Is zero vector always present in any n-dimensional space?

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Discussion Overview

The discussion revolves around the presence of the zero vector in n-dimensional spaces, particularly focusing on vector spaces versus affine spaces. Participants explore whether a plane in 3D space can be considered a vector space if it does not pass through the origin.

Discussion Character

  • Debate/contested

Main Points Raised

  • Some participants reference Gilbert Strang's assertion that every vector space includes the zero vector, questioning if this holds true for planes not passing through the origin.
  • One participant argues that a plane in 3D space is not a vector space unless it passes through the origin, citing closure under addition and scalar multiplication as key criteria.
  • Another participant challenges the understanding of the plane defined by the equation z=2, asserting that it contains all points of the form (x,y,2) where x and y can be any real numbers.
  • Some participants express confusion about the definition of the plane z=2, mistakenly believing it only includes the point (0,0,2).
  • There is a reiteration that if a plane does not pass through the origin, it cannot be classified as a vector space due to the absence of the zero vector.

Areas of Agreement / Disagreement

Participants generally disagree on the implications of a plane not passing through the origin and its classification as a vector space. There is no consensus on the definitions and properties being discussed.

Contextual Notes

Some participants appear to have misunderstandings regarding the definitions of vector spaces and affine spaces, particularly in relation to the closure properties and the nature of planes in 3D space.

Asad Raza
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In the book, Introduction to Linear Algebra, Gilbert Strang says that every time we see a space of vectors, the zero vector will be included in it.

I reckon that this is only the case if the plane passes through the origin. Else wise, how can a space contain a zero vector if it does not pass through the origin?
 
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A plane in 3D space is not a vector space unless it passes through the origin. It is an Affine Space, which is a generalisation of the concept of a vector space.

The reason that a plane that doesn't pass through the origin is not a vector space is that it is not closed under addition or scalar multiplication. Consider the plane ##z=2##, which contains the vectors (0,0,2) and (1,1,2). The sum of those is (1,1,4) which is not in that plane.
 
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Can you kindly explain that how (1,1,2) lies in the plane z=2. The plane z=2 should only contain (0,0,2). No?
 
Asad Raza said:
Can you kindly explain that how (1,1,2) lies in the plane z=2. The plane z=2 should only contain (0,0,2). No?
No. The plane z=2 is the set of all points (x,y,2) where x and y are any real numbers.
 
Asad Raza said:
The plane z=2 should only contain (0,0,2). No?

If it would contain only one point it wouldn't be a plane...
 
Asad Raza said:
Can you kindly explain that how (1,1,2) lies in the plane z=2. The plane z=2 should only contain (0,0,2). No?
To expand on what andrewkirk said, the equation z = 2 means that both x and y are completely arbitrary. You are assuming that since x and y aren't mentioned, both must be zero. Instead, since they aren't present, they can take on any values.
 
I reckon that this is only the case if the plane passes through the origin. Else wise, how can a space contain a zero vector if it does not pass through the origin?
 
If the plane does not pass through the origin then it is not a vector space (according to definition a vector space must contain the zero vector).
 

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