How do i find the basis of subspace U

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SUMMARY

The discussion focuses on finding the basis of subspace U from a given matrix using elementary row operations. The user initially reduces the matrix incorrectly, resulting in an incorrect basis of vectors. The correct reduced form of the matrix should be [1 0 -1 -2; 0 1 2 3; 0 0 0 0], leading to the basis vectors [1 5 -6]^T and [2 6 8]^T, as opposed to the user's output which included an erroneous third vector. The importance of clearly defining the subspace being analyzed is also emphasized.

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  • Elementary row operations in linear algebra
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  • Concept of subspaces in vector spaces
  • Knowledge of basis and dimension in linear algebra
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Homework Statement


In this case find the basis of subspace U
1 2 3 4
5 6 7 8
-6 -8 -10 12

Homework Equations


elementary row operations


The Attempt at a Solution


alright, so i know i have to reduce the matrix and i have done so
1 2 3 4
0 1 2 3
0 0 0 1
now the answer i get is
[1 5 -6]^T [2 6 -8]^T [4 8 12]^T
but the answer in the back of my textbook is
[1 5 -6]^T [2 6 8]^T
what have i done wrong, it seems they have one less column, is it my reduction of the matrix?
 
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You just had an error in reducing your matrix somewhere. Check over your work, because the matrix should have been
1 0 -1 -2
0 1 2 3
0 0 0 0
it was probably a simple algebra mistake.
 
What "subspace U" are you talking about? You give an array of numbers which you refer to as a matrix. I can think of 4 different subspaces that might be meant here:

The row space of the matrix.
The column space of the matrix.
The null space (kernel) of the matrix.
The image of the matrix.

Since you are row-reducing the matrix, you probably mean the column space but it would be a good idea to say so!
 

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