Equation of a Plane in R^n , n>3

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Discussion Overview

The discussion centers on the equation of a plane in R^n for dimensions greater than 3. Participants explore the definitions and representations of planes in higher-dimensional spaces, considering both linear algebraic and geometric perspectives.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how to define a plane in R^n for n>3, noting the challenge of not being able to define a normal vector in these dimensions.
  • Another participant suggests that a plane in R^n could be viewed as the image of a linear map with rank=2, proposing the need for a "flat" embedding of R^2 in R^n.
  • A later reply clarifies that a 2-dimensional plane in R^n could be represented by an equation involving multiple variables, but questions whether a single equation suffices.
  • Another participant argues that identifying an m-dimensional object in n-dimensional space requires n-m numerical equations, thus challenging the idea of using a single equation for a 2-dimensional plane in higher dimensions.
  • It is proposed that a 2-dimensional plane would have n-2 linearly independent normal vectors, and that one could find such a plane by intersecting hyperplanes defined by these normal vectors.

Areas of Agreement / Disagreement

Participants express differing views on how to define and represent a plane in R^n for n>3. There is no consensus on whether a single equation can describe such a plane, and multiple competing perspectives are presented regarding the necessary conditions and definitions.

Contextual Notes

Participants highlight the complexity of defining planes in higher dimensions, noting that assumptions about dimensionality and the nature of equations may influence the discussion. The definitions of normal vectors and the dimensionality of the objects in question remain unresolved.

WWGD
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Hi,

Just curious: what is the equation of a plane in R^n for n>3 ?

We cannot define a normal vector for n>3 , so, what do we do? I thought

of working with flat, embedded copies of R^2 . In terms of linear algebra,

I guess we could see a plane in R^n as any image of a linear map with

rank=2. In terms of geometry, maybe we need a "flat" embedding of R^2

(I am not clear how to make the term 'flat' here more precise) in R^n.

Anyone know?

Thanks.
 
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WWGD said:
Hi,

Just curious: what is the equation of a plane in R^n for n>3 ?

We cannot define a normal vector for n>3 , so, what do we do? I thought

of working with flat, embedded copies of R^2 . In terms of linear algebra,

I guess we could see a plane in R^n as any image of a linear map with

rank=2. In terms of geometry, maybe we need a "flat" embedding of R^2

(I am not clear how to make the term 'flat' here more precise) in R^n.

Anyone know?

Thanks.
In terms of \mathbb{R}^n, then for \boldsymbol{x} = [x_1,x_2,\ldots,x_n]^\text{T}\in\mathbb{R}^n and non-zero scalars a_n the sub-space

\text{const.} = \sum_{i=1}^n a_ix_i

is a hyperplane of \mathbb{R}^n. In actuality, the definition of a hyperplane is more compact: A hyperplane of any vector space is any vector subspace of co-dimension 1.
 
Thganks, but I was thinking of a 2-d plane living in R^n with n higher than 2.

would that still be defined as a1.x1+a2.x2+a3.x3+0x4+...+0.xn=constant?
 
No. It cannot be done with a single equation like that. To identify an m-dimensional object in n-dimensional space requires n- m numerical equations. That is why Hootenanny was able to give a single equation for a hyper-plane (codimension 1 so dimension n- 1). To determine a 2 dimensional plane in n dimensional space would require n- 2 numerical equations.
 
It would have n-2 linearly independent normal vectors. Take the intersection of the hyperplanes passing through a given point, each with one of the normal vectors.
 

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