# Linear Algebra/Basis Vectors

## Definitions

editA **basis** of a vector space **V** is a set of vectors which have the following properties:

- They are linearly independent.
- Their linear combinations build up every vector of
**V**.

A vector space is of **dimension** d if there exists d linearly independent vectors and that any d+1 vectors are linearly dependent.

## Remarkable theorems

edit### Theorem

editIn a vector space of dimension d, any d linearly independent vectors form a basis for that vector space.

#### Proof

editLet there be d vectors. Let **x** be another vector. Then those d vectors and **x** are linearly dependent, so **x** is linearly dependent on those d vectors. Hence, those d vectors form a basis.

### Theorem

editIf a vector space has d vectors for a basis, then it is of dimension d.

#### Proof

edit### Theorem (completion)

editIf you have m linearly independent vectors in a vector space of dimension n (with m<=n), then you can choose n-m vectors which form a basis of the vector space along with the starting m vectors.

#### Proof

editThose m vectors do not form a basis since it is not equal to n, so there exists a vector in the vector space linearly independent of them. Continuing choosing vectors independent of the previous ones in this fashion until one has n vectors.