Why is it not possible for the columns of a matrix to span R^2 even if

In summary, it is not possible for the columns of a matrix to span R^2 if they do not span R^3. This is because even after row-reduction, the resulting matrix may have a rank of 1, which is not enough to span R^2. This is demonstrated by the example given by Bacle where the matrix's columns span R^2 but not R^3.
  • #1
fackert
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Why is it not possible for the columns of a matrix to span R^2 even if those columns do not span R^3?
 
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  • #2


You may end up with a rank-1 matrix after row-reduction.
 
  • #3


fackert said:
Why is it not possible for the columns of a matrix to span R^2 even if those columns do not span R^3?
Is that really what you meant to ask? There is no "why" for a statement that isn't true to begin with! The columns of the matrix
[tex]\begin{bmatrix}1 & 1 & 0 \\ 1 & -1 & 0 \\ 0 & 0 & 0\end{bmatrix}[/tex]
do span R2 but not R3.

(Bacle answered a different question: Why is it possible that the columns of a matrix do not span R2?)
 

Related to Why is it not possible for the columns of a matrix to span R^2 even if

1. Why is it not possible for the columns of a matrix to span R^2 even if the matrix has two columns?

This is because for a set of vectors to span a vector space, they must be linearly independent. If the columns of a matrix span R^2, it means that any vector in R^2 can be written as a linear combination of those columns. However, if the matrix has two columns, it can only span a maximum of two dimensions, which is not enough to cover the entire R^2 space. Therefore, the columns of the matrix cannot span R^2.

2. Can the columns of a matrix span R^2 if the matrix has more than two columns?

No, the columns of a matrix cannot span R^2 even if the matrix has more than two columns. This is because the number of columns in a matrix determines the maximum number of dimensions it can span. So, if the matrix has n columns, it can span a maximum of n dimensions, which is still not enough to span the entire R^2 space.

3. Are there any other conditions that must be met for the columns of a matrix to span R^2?

Yes, in addition to having linearly independent columns, the columns of a matrix must also have the same number of elements as the dimension of the vector space it is trying to span. In the case of R^2, the columns must have two elements. If this condition is not met, the columns of the matrix cannot span R^2.

4. Is it possible for the columns of a matrix to span a vector space of higher dimensions than the number of columns?

Yes, it is possible for the columns of a matrix to span a vector space of higher dimensions than the number of columns. This can happen if the columns are linearly dependent, meaning that one or more columns can be written as a linear combination of the others. In this case, the columns may not span the entire vector space, but they can still span a subset of it.

5. Does the order of the columns in a matrix affect its ability to span a vector space?

Yes, the order of the columns in a matrix can affect its ability to span a vector space. If the columns are not arranged in a way that allows for linear independence, the matrix may not be able to span the vector space. For example, if the first column is a multiple of the second column, the matrix cannot span the entire vector space, even if it has enough columns to do so.

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