Proving Uniqueness of Affine Plane Containing S & Weak-Parallel to T

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Homework Help Overview

The problem involves two affine lines, S and T, in three-dimensional space that are not parallel and do not intersect. The task is to demonstrate the existence and uniqueness of an affine plane R that contains line S and is weakly parallel to line T.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the existence of the plane R and its construction based on the properties of lines S and T. There is a focus on proving the uniqueness of R, with attempts to clarify the implications of the non-parallel nature of S and T.

Discussion Status

Some participants have provided guidance on the uniqueness proof, emphasizing the importance of the non-parallel condition. There is an ongoing exchange about the clarity and elegance of the proposed solutions, with differing opinions on the perceived complexity of the arguments presented.

Contextual Notes

Participants note that S and T are one-dimensional affine lines and that the proof must account for their non-parallelism, which is crucial for establishing the uniqueness of the plane R.

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Homework Statement


[itex]S[/itex] and [itex]T[/itex] are two affine lines in [itex]\mathbb{A}^3[/itex] that are not parallel and [itex]S\cap T=\emptyset[/itex].

Show there is a unique affine plane [itex]R[/itex] that contains [itex]S[/itex] and is weak parallel with [itex]T[/itex].

The Attempt at a Solution


Existence is easy, if [itex]S=p+V[/itex] and [itex]T=q+W[/itex] then [itex]R=p+(V+W)[/itex] satisfies the conditions.

To prove uniqueness I assume planes [itex]R[/itex] and [itex]Q[/itex] both satisfy all conditions. They both contain [itex]S[/itex] so they can be written as [itex]p+(V+vectorspace)[/itex]. That vectorspace must be [itex]W[/itex] since the planes must be weak parallel with [itex]T[/itex]so both [itex]R[/itex] and [itex]Q[/itex] are equal to [itex]p+(V+W)[/itex].

Is this good?
If it is, it still seems very ugly to me, is there a better way to do it?

Thanks
Alex
 
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What is ugly about the solution?? It seems nice...

There is a little detail missing though. For uniqueness, you must use somewhere that S and T are not parallel.
 
Thanks micromass!

Ok,The direction of R and Q must contain W, since V does not contain W, and is not a subspace of W (S and T are not parrallel and have dimensions 1) , "vectorspace" must be W
good now?

I feel it's ugly because it largely repeats the construction for existence.

thanks again.
 
A_B said:
Thanks micromass!

Ok,The direction of R and Q must contain W, since V does not contain W, and is not a subspace of W (S and T are not parrallel and have dimensions 1) , "vectorspace" must be W
good now?

That's better.

I feel it's ugly because it largely repeats the construction for existence.

That's exactly why I think it's a pretty argument :smile:
 

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