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**123ronnie321****Member**- Registered: 2010-09-28
- Posts: 128

Let V be a vector space and A,B be subsets of V .

prove that: span (A U B) = span (A) + span (B)

looks pretty obvious but dont know how to prove it using math

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

Hi 123ronnie321

I don't think that's true. Look at A={(1,0,0),(0,1,0)} and B={(1,0,0),(0,0,1)}, for example.

, on the other hand, is true.*Last edited by anonimnystefy (2013-02-25 18:14:28)*

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Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

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**scientia****Member**- Registered: 2009-11-13
- Posts: 224

I think 123ronnie321 is looking for the direct sum, not the union.

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,037

Ah, I am sorry, then.

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

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