Zero Vector Space Product iff Factor is Zero/Proof 1
Jump to navigation
Jump to search
Theorem
Let $F$ be a field whose zero is $0_F$ and whose unity is $1_F$.
Let $\struct {\mathbf V, +, \circ}_F$ be a vector space over $F$, as defined by the vector space axioms.
Let $\mathbf v \in \mathbf V, \lambda \in F$.
Then:
- $\lambda \circ \mathbf v = \bszero \iff \paren {\lambda = 0_F \lor x = \bszero}$
Proof
A vector space is a module, so all results about modules also apply to vector spaces.
So from Scalar Product with Identity it follows directly that:
- $\lambda = 0_F \lor \mathbf v = e \implies \lambda \circ \mathbf v = \bszero$
Next, suppose $\lambda \circ \mathbf v = \bszero$ but $\lambda \ne 0_F$.
Then:
\(\ds \bszero\) | \(=\) | \(\ds \lambda^{-1} \circ \bszero\) | Zero Vector Scaled is Zero Vector | |||||||||||
\(\ds \) | \(=\) | \(\ds \lambda^{-1} \circ \paren {\lambda \circ \mathbf v}\) | as $\lambda \circ \mathbf v = \bszero$ | |||||||||||
\(\ds \) | \(=\) | \(\ds \paren {\lambda^{-1} \circ \lambda} \circ \mathbf v\) | Vector Space Axiom $\text V 7$: Associativity with Scalar Multiplication | |||||||||||
\(\ds \) | \(=\) | \(\ds 1 \circ \mathbf v\) | Field Axiom $\text M4$: Inverses for Product | |||||||||||
\(\ds \) | \(=\) | \(\ds \mathbf v\) | Vector Space Axiom $\text V 8$: Identity for Scalar Multiplication |
$\blacksquare$
Sources
- 1965: Seth Warner: Modern Algebra ... (previous) ... (next): Chapter $\text {V}$: Vector Spaces: $\S 26$. Vector Spaces and Modules: Theorem $26.2 \ (8)$
- 1969: C.R.J. Clapham: Introduction to Abstract Algebra ... (previous) ... (next): Chapter $7$: Vector Spaces: $\S 32$. Definition of a Vector Space: Theorem $64 \ \text{(vi)}$