Let v1,v2,...,vm, w is linearly dependent and let
w∈span(v1,v2,...vm)
w=α1v1+α2v2+....+αmvm=0, Where at least one of αi=0.
⇒α1v1+α2v2+....+αmvm−w=0
⇒α1v1+α2v2+....+αmvm+αm+1w=0, Where αm+1=−1=0
So, (v1,v2,...vm ), w are linearly independent which is contradiction.
Hence, w∈span((v1,v2,...vm)
Conversely: Let w∈span(v1,v2,..,vm)
TO show: x1,x2...,xm,w is linearly independent
then, α1,α2,.....,αm+1=0
Such that,
α1v1+α2v2+....+αmvm+αm+1w=0
say αm+1=0.
αm+1w=−α1v1−α2v2....−αmvm
w=−α1αm+1−1v1−α2αm+1−12v2....−αmαm+1−1vm
w∈span(v1,v2,...,vm), Which is contradiction.
Hence , v1,v2,...,vm,w is linearly independent.
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