# How many vectors in span({v})

1. Sep 16, 2009

### brru25

1. The problem statement, all variables and given/known data

Let v be an element of F2p \ {(0,0)}. How many vectors does Span({v}) have? How many 1-dimensional vector subspaces does F2p have?

F2p is the two-dimensional field (a,b) where each a, b are elements of Fp, where p is a prime number.

3. The attempt at a solution

I know the total number of elements in the vector space F2p \ {(0,0)} is p2 - 1. I also thought that this was the number of vectors in Span({v}) but I've told by a couple people that is not so. I started with the definition of span but I just couldn't see the rest unfold.

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Sep 16, 2009

### Office_Shredder

Staff Emeritus
An element in span(v) must be of the form av for some a in the field. How many choices of a do you have? Do all of these choices yield a different vector, or can av=bv if a=/=b?

3. Sep 16, 2009

### Dick

Take an example. Let F=Z_3, the field with three elements {0,1,2}. Yes, there are 8 elements in (Z_3)^2-{0,0}. How many elements are in span((1,1))? That's (1,1)*x for all x in Z_3. Does that help you to see things unfold?

4. Sep 16, 2009

### brru25

Would (1,1)*x have 3 elements? (1,1,0), (1,1,1), (1,1,2)? Or am I reading this incorrectly?

5. Sep 16, 2009

### Dick

Well, yeah. Would have three elements. But they would be (0,0)=(1,1)*0, (1,1)=(1,1)*1 and (2,2)=(1,1)*2.

6. Sep 16, 2009

### brru25

Okay now I see what you meant sorry about that.

7. Sep 16, 2009

### brru25

"a" I believe can be any number in F.