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MATH
[1251]

Theorems from Basis and dimension

All theorems from Basis and dimension.

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Representation in a basis

If B={u1,…,un}B=\{u_1,\ldots,u_n\} is a basis for VV, then every vector v∈Vv\in V has a unique representation

v=λ1u1+⋯+λnun,λ1,…,λn∈F.v=\lambda_1u_1+\cdots+\lambda_nu_n, \qquad \lambda_1,\ldots,\lambda_n\in F.

Spanning sets count against independent sets

Let SS and LL be finite subsets of a vector space VV. If span⁡(S)=V\operatorname{span}(S)=V and LL is linearly independent, then

∣S∣≥∣L∣.|S|\geq |L|.

All bases have the same size

Any two finite bases of a vector space contain the same number of vectors.

Counting with dimension

Let VV be finite-dimensional.

  1. If a set SS of nn vectors spans VV, then n≥dim⁡(V)n\geq\dim(V). If n=dim⁡(V)n=\dim(V), then SS is a basis.
  2. If a set SS of mm vectors is linearly independent in VV, then m≤dim⁡(V)m\leq\dim(V). If m=dim⁡(V)m=\dim(V), then SS is a basis.

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