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Section II. <strong>Linear</strong> Independence 107<br />

1.14 Example Here are some linearly independent sets from R3 and their<br />

supersets.<br />

⎛<br />

(1) If S1 = { ⎝ 1<br />

⎞<br />

0⎠}<br />

then the span [S1] isthex-axis.<br />

0<br />

A linearly dependent superset:<br />

⎛<br />

{ ⎝ 1<br />

⎞ ⎛<br />

0⎠<br />

, ⎝<br />

0<br />

−3<br />

⎞<br />

0 ⎠}<br />

A linearly independent superset:<br />

⎛<br />

0<br />

{ ⎝ 1<br />

⎞ ⎛<br />

0⎠<br />

, ⎝<br />

0<br />

0<br />

⎞<br />

1⎠}<br />

0<br />

⎛ ⎞ ⎛ ⎞<br />

1 0<br />

(2) If S2 = { ⎝0⎠<br />

, ⎝1⎠}<br />

then [S2] isthexy-plane.<br />

0 0<br />

⎛ ⎞<br />

1<br />

⎛ ⎞<br />

0<br />

⎛ ⎞<br />

3<br />

A linearly dependent superset: { ⎝0⎠<br />

, ⎝1⎠<br />

, ⎝−2⎠}<br />

⎛<br />

0<br />

⎞<br />

1<br />

⎛<br />

0<br />

⎞<br />

0<br />

⎛<br />

0<br />

⎞<br />

0<br />

A linearly independent superset: { ⎝0⎠<br />

, ⎝1⎠<br />

, ⎝0⎠}<br />

0 0 1<br />

⎛ ⎞ ⎛ ⎞ ⎛ ⎞<br />

1 0 0<br />

(3) If S3 = { ⎝0⎠<br />

, ⎝1⎠<br />

, ⎝0⎠}<br />

then [S3] is all of R<br />

0 0 1<br />

3 .<br />

⎛ ⎞ ⎛ ⎞ ⎛ ⎞ ⎛ ⎞<br />

1 0 0 2<br />

A linearly dependent superset: { ⎝0⎠<br />

, ⎝1⎠<br />

, ⎝0⎠<br />

, ⎝−1⎠}<br />

0 0 1 3<br />

There are no linearly independent supersets.<br />

(Checking the dependence or independence of these sets is easy.)<br />

So in general a linearly independent set can have some supersets that are dependent<br />

and some supersets that are independent. We can characterize when a<br />

superset of a independent set is dependent and when it is independent.<br />

1.15 Lemma Where S is a linearly independent subset of a vector space V ,<br />

S ∪{�v} is linearly dependent if and only if �v ∈ [S]<br />

for any �v ∈ V with �v �∈ S.

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