Subspace Intersection Problem: Proving W1 and W2 in R^n

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In summary, to prove that the intersection of two subspaces W1 and W2 in R^n is also a subspace, one must show that W is closed under addition and scalar multiplication. To do this, it is necessary to take two arbitrary vectors u1 and u2 in W and show that their sum is also in W, as well as take an arbitrary scalar s and show that su1 is also in W. This can be expressed in mathematical terms as: suppose u and v are in W, then u+v is in W1 and W2, and therefore in W.
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mlarson9000
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Homework Statement



Let W1 and W2 be two subspaces of R^n. Prove that their intersection is also a subspace.

Homework Equations





The Attempt at a Solution



I know that in R^2 and R^3 the intersection would be the origin, which would be the zero vector, which would be a subspace, but I don't know how to make a general argument about this.
 
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Let W be the intersection of W1 and W2. Is the vector space W closed under addition and scalar multiplication?
 
  • #3
VeeEight said:
Let W be the intersection of W1 and W2. Is the vector space W closed under addition and scalar multiplication?

Wouldn't it have to be? If W is in both W1 and W2, which are both subspaces and therefore closed under addition and scalar multiplication, wouldn't W be also? If so, I still don't know exactly how to say that in Math speak.
 
  • #4
mlarson9000 said:
Wouldn't it have to be?
Well, if not, you're going to have a tough time proving it.
mlarson9000 said:
If W is in both W1 and W2, which are both subspaces and therefore closed under addition and scalar multiplication, wouldn't W be also?
Take a couple of arbitrary vectors u1 and u2 in W, and show that their sum is also in W. Then take an arbitrary scalar s, and show that su1 is in W. That's how you would do it it "math speak."
mlarson9000 said:
If so, I still don't know exactly how to say that in Math speak.
 
  • #5
mlarson9000 said:
Wouldn't it have to be? If W is in both W1 and W2, which are both subspaces and therefore closed under addition and scalar multiplication, wouldn't W be also? If so, I still don't know exactly how to say that in Math speak.
Suppose u and v are in W. Then u and v are both is W1 and, since W1 is a subspace, u+ v is in W1. Also u and v are both in W2 ...
 

1. What is the Subspace Intersection Problem?

The Subspace Intersection Problem is a mathematical problem that involves finding the intersection between two subspaces in a vector space. In other words, it is the process of determining if two subspaces share any common vectors.

2. What is the significance of proving W1 and W2 in R^n?

Proving W1 and W2 in R^n is important because it helps us understand the relationship between two subspaces and how they interact with each other. It also allows us to determine if the two subspaces are independent or not.

3. How do you prove W1 and W2 in R^n?

To prove W1 and W2 in R^n, you can use the method of contradiction. Assume that the two subspaces share a common vector and then show that this leads to a contradiction. This proves that the two subspaces do not share any common vectors and are therefore independent.

4. Can the Subspace Intersection Problem be solved in any vector space?

Yes, the Subspace Intersection Problem can be solved in any vector space. However, the process and methods for proving W1 and W2 may vary depending on the dimensionality and properties of the vector space.

5. How is the Subspace Intersection Problem relevant in real-world applications?

The Subspace Intersection Problem has many practical applications, such as in image processing, signal processing, and data compression. It is also used in machine learning and computer vision to determine the relationship between different data sets and identify common features.

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