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Homework Statement
Prove that if a∈F (where F represents ℝ or ℂ), v∈V (where V is a vector space) and av = 0, then a= 0 or v = 0.
Homework Equations
The axioms for a vector space may be relevant.
The Attempt at a Solution
Case 1 (v = 0):
Suppose that a∈F, v∈V, and av = 0.
Also, let u∈F.
Then av + au = au (added au to both sides)
So a(v + u) = au (distributive property)
And v + u = u (multiplied both sides by 1/a)
Therefore v = 0.
Case 2 (a = 0):
Suppose that a∈F, v∈V, and av = 0.
I'm stuck here.
The book proves this statement slightly different. For Case 1, the author simply assumes a ≠ 0 and he may therefore multiply both sides by 1/a to get v = 0. For Case 2, the author more or less says av = 0 when a = 0 just because, without any kind of justification.
On a side note, I just finished a proofs book and began self-studying linear algebra for mathematicians. The above problem is from Linear Algebra Done Right (by Axler), which I recently read is targeted at graduate students. As an undergraduate, I'm having a hell of a time so far with this book. If anyone can recommend a more intermediate linear algebra book (undergraduate level, with proofs) I'd surely appreciate it. Thanks in advance.