Showing H is a Subspace of M2x2

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In summary, the conversation discusses the dimensions and basis of the space H, which is a subset of M2x2. It is determined that a basis for M2x2 would have 4 components, but it is uncertain how many components a basis for H would have. The conversation then goes on to discuss whether the given matrices span H and the steps needed to show that H is a subspace of M2x2.
  • #1
judahs_lion
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H = ([a,b;c,d] : a+d =0}

Dim(M2x2)= 4, so a basis would have 4 components?

I got this far and am stuck.

[a, b ; c , -a] = a[1,0; 0,-1] + b[0, 1;0,0] +c[0,0; 1,0]
 
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  • #2


judahs_lion said:
H = ([a,b;c,d] : a+d =0}

Dim(M2x2)= 4, so a basis would have 4 components?
A basis for M2x2 would have 4 vectors/matrices, but how many would be in a basis for H?
judahs_lion said:
I got this far and am stuck.

[a, b ; c , -a] = a[1,0; 0,-1] + b[0, 1;0,0] +c[0,0; 1,0]

Now, do these matrices span H? I.e., can every matrix in H be written as a linear combination of the three matrices above?

What's left to do is to show that H is a subspace of M2x2. To do this, you need to show three things:
That the zero matrix is in H.
That if A and B are in H, then A + B is in H.
That if A is in H and c is a scalar, then cA is in H.
 
  • #3


Thank you
 

FAQ: Showing H is a Subspace of M2x2

What does it mean for H to be a subspace of M2x2?

For H to be a subspace of M2x2, it must satisfy three conditions: it must contain the zero vector, it must be closed under vector addition, and it must be closed under scalar multiplication. This means that any vector in H must also be in M2x2, and the sum of any two vectors in H must also be in H. Additionally, multiplying any vector in H by a scalar must result in another vector in H.

How can I prove that H is a subspace of M2x2?

To prove that H is a subspace of M2x2, you must show that it satisfies all three conditions mentioned above. You can do this by taking an arbitrary vector in H and showing that it is also in M2x2, as well as showing that the sum of any two vectors in H is also in H and that multiplying any vector in H by a scalar results in another vector in H.

Can H be a subspace of M2x2 if it does not contain the zero vector?

No, the zero vector is a necessary component of a subspace. Without it, the subspace would not be closed under scalar multiplication, as multiplying any vector by 0 would result in a vector outside of the subspace.

Is it possible for H to be a subspace of M2x2 if it is not closed under vector addition?

No, a subspace must be closed under vector addition in order for it to be a valid subspace. If the sum of two vectors is not in H, then H would not satisfy the condition of being closed under vector addition.

What is the difference between a subspace and a subset?

A subset is a collection of elements that are part of a larger set. A subspace, on the other hand, is a subset that also satisfies certain conditions, such as being closed under vector addition and scalar multiplication. In other words, all subspaces are subsets, but not all subsets are subspaces.

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