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Linear Combination
A linear combination of the vectors {v1,…,vm} of vectors in a vector space V is: a1v1+…+amvm where a1,…,am∈𝔽
Span
The set of all linear combinations of the vectors {v1,…,vm}⊆V (where V is a vector space) called the span of {v1,…,vm} and we define the notation: span⁡({v1,...,vm}):={a1v1+…+amvm:a1,...,am∈𝔽} we define span⁡(∅):={0}
Linearly Independent
Let V be a vector space over a field F. A set of vectors {v1,…,vm}⊆V is linearly independent if, for scalars a1,…,am∈F, the only solution to ∑i=1maivi=0 is a1=⋯=am=0. We define ∅ to be linearly independent.
A Set Containing Zero Is Not Linearly Independent
Let V be a vector space over a field F, and let S={v1,…,vm}⊆V. If 0∈S, then S is not linearly independent.
Choose j with vj=0. Set aj=1 and ai=0 for every i≠j. Then ∑i=1maivi=1⋅vj+∑i≠j0⋅vi=0, even though aj≠0. This contradicts the definition of linear independence.
General Linear Independence
A set S⊆V is said to be generally linearly independent if for every every finite subset F⊆S, F is linearly indepenent
Spanning Set
Suppose that V is a vector space, then we say that S is a spanning set of V if span⁡(S)=V
Linearly Independent iff Unique Representation
{v1,…,vm} is linearly independent iff each vector in the set {v1,…,vm} has only one representation as a linear combination of {v1,…,vm}
Linearly Dependent
{v1,…,vm}⊆V is said to be linearly dependent if it is not linearly independent
Linearly Depedent iff Zero has a Non-Trivial Representation
{v1,…,vm}⊆V is linearly dependent iff there exists a1,…,am∈𝔽 and i∈[1,m] where ai≠0 such that ∑i=1maivi=0