Proof Help: Showing S perp contains V perp when S is a subspace of V

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In summary, the conversation discusses how to prove that if a subspace S is contained in a subspace V, then S perp contains V perp. The key is to show that if x is in V perp, then it is also in S perp, which is a straightforward argument since S is a subset of V.
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Homework Statement



Can someone help me with this proof? I'm supposed to show that if a subspace S is contained in subspace V, then S perp contains V perp.

Homework Equations



None, or the dimensions must add up, so S + S perp = some dimension N, and V + V perp equals the same dimension N, if S and V are both subspaces of N.

The Attempt at a Solution



Am I supposed to show that the dimensions don't add up? Can anyone provide suggestions? Thanks.
 
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  • #2
S perp contains V perp iff x in V perp implies x in S perp.
x in V perp iff for all y in V, <x,y> = 0.
x in S perp iff for all y in S, <x,y> = 0.

So you want to show (for all y in V, <x,y> = 0) implies (for all y in S, <x,y> = 0). Well S is a subset of V, so this is obvious.
 

1. What is the definition of "perpendicular" in the context of subspaces?

Two subspaces are said to be perpendicular if every vector in one subspace is orthogonal (or perpendicular) to every vector in the other subspace.

2. Why is it important to show that S perp contains V perp when S is a subspace of V?

This proof helps to establish the relationship between two subspaces and their orthogonal complements. It is a fundamental concept in linear algebra and is used in various applications, such as finding solutions to systems of linear equations and understanding the properties of vector spaces.

3. How do we show that S perp contains V perp?

To show that S perp contains V perp, we need to prove that every vector in V perp is also in S perp. This can be done by showing that the dot product of any vector in V perp with any vector in S is equal to 0. This implies that the vector is orthogonal to every vector in S, and therefore, is also in S perp.

4. Can we assume that both S and V are subspaces of the same vector space?

Yes, in this proof, we assume that both S and V are subspaces of the same vector space. This is because the concept of perpendicular subspaces only applies when the subspaces exist within the same vector space.

5. Are there any specific properties of subspaces that we can use to prove that S perp contains V perp?

Yes, there are specific properties of subspaces that can be used in this proof. One important property is that the orthogonal complement of a subspace is also a subspace. This means that if S is a subspace of V, then S perp is also a subspace of V.

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