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Homework Help: Linear Algebra - subset spanning R^4

  1. Oct 24, 2011 #1
    1. The problem statement, all variables and given/known data

    Let S={(1,2,3,4),(-1,2,0,1),(1,0,1,1),(-2,2,1,0)}. Determine whether or not S is linearly independent. If not, write one of the vectors in S as a linear combination of the others. Find a subset of S which is a basis of the subspace of R4 spanned by S.

    3. The attempt at a solution
    I put the 4 vectors into matrix form, and reduced it to get:
    [1 2 3 4]
    [0 2 2 3]
    [0 0 -1 -1]
    [0 0 0 -2]
    So they are linearly independant. Since S has a rank of 4, it spans R4. So any basis of the subspace of R4 should be spanned by S.
    My subset of S which is a basis of the subspace of R4 and spanned by S is:

    Is this correct? I'm not quite sure what they mean by a subset of S.
  2. jcsd
  3. Oct 24, 2011 #2


    Staff: Mentor

    Yes, the vectors in S are linearly independent, so they span R4.

    Their question was hypothetical, in case the vectors in S were linearly dependent. If that had been true they wanted you to find the largest set of linearly independent vectors in S, which would have been a basis for some subspace of R4.
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