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STATISTICS 512 TECHNIQUES OF MATHEMATICS FOR ...

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18<br />

• Asubset of R that is itself closed under addition<br />

and scalar multiplication is a vector space<br />

in its own right, called a vector subspace of R ;<br />

similarly ⊂ closed under addition and scalar<br />

multiplication is a subspace of . (You might<br />

wish to prove this; the proof consists of showing<br />

that 1.-8. hold in if they hold in R and if <br />

has these two closure properties.)<br />

• Definitions:<br />

(i) Elements v 1 v of form a spanning set<br />

if every v ∈ is a linear combination of them.<br />

(ii) Elements v 1 v of are (linearly) independent<br />

if all are non-zero and<br />

X<br />

v = 0 ⇒ all =0<br />

i.e. there is only one way in which 0 can be represented<br />

as a linear combination of them. Otherwise<br />

they are dependent (equivalently, at least<br />

one is a linear combination of the others).<br />

(iii) A spanning set whose elements are independent<br />

is a basis of . Thus if {v 1 v } is a<br />

basis, any v ∈ is uniquely (why?) representable<br />

as a linear combination of these basis elements.

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