Checking if sets are subspaces of ##\mathbb{R}^{3}##

In summary, the set W = {x, y, z | x ≤ y ≤ z} is a subspace of ℝ3 because it satisfies the three properties of containing the zero vector, being closed under scalar multiplication, and being closed under addition. To prove this, we can take arbitrary vectors from the set and show that they also satisfy these properties.
  • #1
yango_17
60
1

Homework Statement


Is the set ##W## a subspace of ##\mathbb{R}^{3}##?
##W=\left \{ \begin{bmatrix}
x\\
y\\
z
\end{bmatrix}:x\leq y\leq z \right \}##

Homework Equations

The Attempt at a Solution


I believe the set is indeed a subspace of ##\mathbb{R}^{3}##, since it looks like it will satisfy the three properties of a subspace. I'm wondering as to how one would go about explicitly proving this. Any help would be appreciated. Thanks.
 
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  • #2
yango_17 said:

Homework Statement


Is the set ##W## a subspace of ##\mathbb{R}^{3}##?
##W=\left \{ \begin{bmatrix}
x\\
y\\
z
\end{bmatrix}:x\leq y\leq z \right \}##

Homework Equations

The Attempt at a Solution


I believe the set is indeed a subspace of ##\mathbb{R}^{3}##, since it looks like it will satisfy the three properties of a subspace. I'm wondering as to how one would go about explicitly proving this. Any help would be appreciated. Thanks.
What are the three properties you need to verify? You didn't list them in the 2nd section or anywhere else.

Generally, you take one or two arbitrary members of your set and show that the set is closed under addition and scalar multiplication.
 
  • #3
So, the properties would be that the set needs to contain the zero vector, needs to be closed under scalar multiplication, and needs to be closed under addition. When you say take arbitrary members of the set to test the last two properties, what exactly do you mean?
 
  • #4
yango_17 said:
So, the properties would be that the set needs to contain the zero vector, needs to be closed under scalar multiplication, and needs to be closed under addition. When you say take arbitrary members of the set to test the last two properties, what exactly do you mean?
Let, say, ##\vec{u}## and ##\vec{v}## be elements of W, with ##\vec{u} = <u_1, u_2, u_3>## and ##\vec{v} = <v_1, v_2, v_3>##.
What condition do these vectors need to satisfy in order to belong to set W? You are given this condition.

Is 0 an element of W?
If ##\vec{u}## and ##\vec{v}## are arbitrary members of W, is ##\vec{u} + \vec{v}## also in W?
If ##\vec{u}## is an arbitrary member of W, and k is an arbitrary scalar, is ##k\vec{u}## also in W?

If the answers to these questions are all "yes", then the set is a subspace of ##\mathbb{R}^3##.
 

Related to Checking if sets are subspaces of ##\mathbb{R}^{3}##

1. What is a subspace of ##\mathbb{R}^{3}##?

A subspace of ##\mathbb{R}^{3}## is a subset of ##\mathbb{R}^{3}## that satisfies three conditions: it contains the zero vector, it is closed under vector addition, and it is closed under scalar multiplication. In other words, a subspace is a smaller vector space that is contained within a larger vector space.

2. How do you check if a set is a subspace of ##\mathbb{R}^{3}##?

To check if a set is a subspace of ##\mathbb{R}^{3}##, you need to verify that it satisfies the three conditions mentioned above. This means checking if the set contains the zero vector, if it is closed under vector addition, and if it is closed under scalar multiplication. If all three conditions are met, then the set is a subspace of ##\mathbb{R}^{3}##.

3. Can a subspace of ##\mathbb{R}^{3}## be a line or a plane?

Yes, a subspace of ##\mathbb{R}^{3}## can be a line or a plane. As long as the set satisfies the three conditions of a subspace, it can be any size or shape within ##\mathbb{R}^{3}##. For example, the x-y plane or the line y = 2x are both subspaces of ##\mathbb{R}^{3}##.

4. What is the difference between a subspace and a span?

A subspace is a subset of a vector space that satisfies certain conditions, while a span is the set of all possible linear combinations of a given set of vectors. In other words, a subspace is a specific type of set within a vector space, while a span is a mathematical concept used to describe a set of vectors.

5. Can a set be a subspace of ##\mathbb{R}^{3}## if it does not contain the zero vector?

No, a set cannot be a subspace of ##\mathbb{R}^{3}## if it does not contain the zero vector. The zero vector is a necessary condition for a set to be a subspace, as it is required for the set to be closed under scalar multiplication and vector addition. Without the zero vector, the set cannot be considered a subspace of ##\mathbb{R}^{3}##.

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