Chapter 5: Problem 24
Let \(T: V \rightarrow V\) be a linear transformation of a vector space \(V\) into itself, and let \(\lambda\) be a scalar. Prove that \(\\{\mathbf{v} \in V \mid T(\mathbf{v})=\lambda \mathbf{v}\\}\) is a subspace of \(V\).
Short Answer
Expert verified
The set \( \{\mathbf{v} \in V \mid T(\mathbf{v}) = \lambda \mathbf{v} \} \) is a subspace of \( V \).
Step by step solution
01
Define the Set
Let \( W = \{\mathbf{v} \in V \mid T(\mathbf{v}) = \lambda \mathbf{v} \} \). We need to prove that \( W \) is a subspace of \( V \). A subset of a vector space is a subspace if it is closed under addition and scalar multiplication, and contains the zero vector.
02
Verify the Zero Vector in W
To check if the zero vector \( \mathbf{0} \) is in \( W \), apply the transformation: \( T(\mathbf{0}) = 0 = \lambda \cdot \mathbf{0} \). Since \( T(\mathbf{0}) = \lambda \cdot \mathbf{0} \), the zero vector is indeed in \( W \).
03
Check Closure Under Addition
Take any \( \mathbf{u}, \mathbf{v} \in W \). By definition, \( T(\mathbf{u}) = \lambda \mathbf{u} \) and \( T(\mathbf{v}) = \lambda \mathbf{v} \). Consider \( \mathbf{u} + \mathbf{v} \). Then:\[ T(\mathbf{u} + \mathbf{v}) = T(\mathbf{u}) + T(\mathbf{v}) = \lambda \mathbf{u} + \lambda \mathbf{v} = \lambda (\mathbf{u} + \mathbf{v}) \]Therefore, \( \mathbf{u} + \mathbf{v} \in W \).
04
Check Closure Under Scalar Multiplication
Take any \( \mathbf{v} \in W \) and any scalar \( c \). Since \( T(\mathbf{v}) = \lambda \mathbf{v} \), consider \( c\mathbf{v} \). Then:\[ T(c\mathbf{v}) = cT(\mathbf{v}) = c(\lambda \mathbf{v}) = \lambda (c\mathbf{v}) \]Thus, \( c\mathbf{v} \in W \).
05
Conclusion
Since \( W \) contains the zero vector, is closed under addition, and closed under scalar multiplication, \( W \) is a subspace of \( V \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vector Space
Imagine a vector space as a playground for vectors. It is a collection of objects called vectors, along with two operations: vector addition and scalar multiplication.
- Vector addition allows you to combine two vectors, producing another vector in the same space.
- Scalar multiplication lets you stretch or shrink a vector using a number (a scalar).
- There is always a zero vector, which acts as an additive identity.
- The space is closed under addition and scalar multiplication, meaning that combining vectors or scaling them stays inside the space.
Subspace
A subspace is like a smaller playground within a bigger vector space. It itself forms a vector space and obeys the same rules.
A subspace of a vector space is a set of vectors that satisfies the following:
A subspace of a vector space is a set of vectors that satisfies the following:
- Contains the zero vector.
- Closed under addition: If you take any two vectors in this set, their sum is also in the set.
- Closed under scalar multiplication: If you multiply any vector in the subspace by any scalar, the result still lies in the subspace.
Scalar Multiplication
Scalar multiplication is like changing the size of a vector without altering its direction.
If you imagine a vector as an arrow, scalar multiplication stretches or compresses the arrow. Consider multiplying a vector by a positive scalar — it increases or decreases its length while maintaining its original direction.
If you imagine a vector as an arrow, scalar multiplication stretches or compresses the arrow. Consider multiplying a vector by a positive scalar — it increases or decreases its length while maintaining its original direction.
- If the scalar is negative, the vector also flips direction but preserves its magnitude change.
- If the scalar is zero, the vector "disappears" into the zero vector.
Closure Properties
Closure properties are like the safety rules on the playground, ensuring you stay within the limits.
For a set of vectors to be considered a vector space or subspace, it must be closed under two main operations: addition and scalar multiplication.
For a set of vectors to be considered a vector space or subspace, it must be closed under two main operations: addition and scalar multiplication.
- Closed under addition means that adding any two vectors in the set results in another vector that still belongs to the set.
- Closed under scalar multiplication means any vector in the set, when multiplied by a scalar, remains in the set.