Linear algebra help: Subspaces

In summary, we need to prove that for matrices A and B, where C denotes column space, C(AB) is a subset of C(A). This can be done by showing that for any vector u in C(AB), there exists a corresponding vector v in C(A) such that Av = u. This can be done by using the definition of column space and the fact that ABx = u for some x in Rp.
  • #1
epkid08
264
1

Homework Statement


Prove that C(AB) is a subset of C(A) for matrices A,B, where C denotes column space.


Homework Equations


C(AB) = {b \in \mathbbcode{R}^m: Ax=b is consistent}


The Attempt at a Solution


I don't really know where to start.
 
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  • #2
What's the definition of a subset?
 
  • #3
to make things easier suppose that A is mxn, and B is nxp. so AB is mxp.

now..hint: suppose u is in C(AB), which means that ABx = u, for some x in Rp.

can you think of some vector v in Rn, with Av = u?

(what mapping do we know for sure produces a vector in Rn?)
 

What is a subspace in linear algebra?

A subspace in linear algebra is a subset of a vector space that satisfies all of the properties of a vector space. This means that it must be closed under vector addition and scalar multiplication, and it must contain the zero vector.

How do I determine if a set is a subspace?

To determine if a set is a subspace, you must check if it satisfies the three properties of a vector space: closure under vector addition, closure under scalar multiplication, and the presence of the zero vector. If all three properties are met, then the set is a subspace.

What is the difference between a subspace and a span?

A subspace is a subset of a vector space that satisfies all of the properties of a vector space. A span, on the other hand, is the set of all possible linear combinations of a given set of vectors. In other words, a subspace is a subset of a vector space, while a span is a collection of vectors within a vector space.

Can a subspace have more than one basis?

Yes, a subspace can have more than one basis. A basis is a set of linearly independent vectors that span the entire subspace. Since there can be multiple sets of linearly independent vectors that span the same subspace, there can be more than one basis for a subspace.

How can I find the dimension of a subspace?

The dimension of a subspace is equal to the number of vectors in its basis. Therefore, to find the dimension of a subspace, you can find a set of linearly independent vectors that span the subspace and count the number of vectors in that set.

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