Question #193599

Suppose v1v2..vmis linearly independent in V and w element of V. Show that v1,v2,...vm;w is linearly independent if and only if w = not element of span(v1,v2,...vm).


1
Expert's answer
2021-05-17T18:56:46-0400

Let v1,v2,...,vm,v_1,v_2,...,v_m, w is linearly dependent and let

wspan(v1,v2,...vm)w\in span(v_1,v_2,...v_m)


w=α1v1+α2v2+....+αmvm=0,w=\alpha_1v_1+\alpha_2v_2+....+\alpha_mv_m=0, Where at least one of αi0.\alpha_i\neq 0.


α1v1+α2v2+....+αmvmw=0\Rightarrow \alpha_1v_1+\alpha_2v_2+....+\alpha_mv_m-w=0


α1v1+α2v2+....+αmvm+αm+1w=0, Where αm+1=10\Rightarrow \alpha_1v_1+\alpha_2v_2+....+\alpha_mv_m+\alpha_{m+1}w=0,\text{ Where }\alpha_{m+1}=-1\neq 0


So, (v1,v2,...vmv_1,v_2,...v_m ), w are linearly independent which is contradiction.

Hence, wspan((v1,v2,...vm)w\in span((v_1,v_2,...v_m)


Conversely: Let wspan(v1,v2,..,vm)w \in span(v_1,v_2,..,v_m)


TO show: x1,x2...,xm,wx_1,x_2...,x_m , w is linearly independent

then, α1,α2,.....,αm+10\alpha_1,\alpha_2,.....,\alpha_{m+1}\neq 0


Such that,

 α1v1+α2v2+....+αmvm+αm+1w=0\alpha_1v_1+\alpha_2v_2+....+\alpha_mv_m+\alpha{m+1}w=0


 say αm+10.\alpha_{m+1}\neq 0.


αm+1w=α1v1α2v2....αmvm\alpha_{m+1} w=-\alpha_1v_1-\alpha_2v_2.... -\alpha_mv_m


w=α1αm+11v1α2αm+112v2....αmαm+11vmw=-\alpha_1\alpha^{-1}_{m+1}v_1-\alpha_2\alpha^{-1}_{m+1}2v_2.... -\alpha_m\alpha^{-1}_{m+1}v_m


wspan(v1,v2,...,vm),w\in span(v_1,v_2,...,v_m), Which is contradiction.


Hence , v1,v2,...,vm,wv_1,v_2,...,v_m , w is linearly independent.


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