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Homework Statement
Let S be a subset of [itex]R^{4}[/itex]:
S = {[itex]v_{1}[/itex],[itex]v_{2}[/itex], [itex]v_{3}[/itex], [itex]v_{4}[/itex]} = { [1,3,2,0] [-2,0,6,7] [0,6,10,7] [2,10,-3,1] }
Determine whether S spans [itex]R^{4}[/itex].
Homework Equations
span(S) = {V| V = a[itex]v_{1}[/itex]+b[itex]v_{2}[/itex]+c[itex]v_{3}[/itex]+d[itex]v_{4}[/itex]}
The Attempt at a Solution
When I row reduce the matrix A, whose rows are the vectors in S, I get a matrix whose rank = 3. So I conclude that S does NOT span [itex]R^{4}[/itex]. Is this correct? If so, why? Let me explore a little further.
Let B = rref(A) =
1 0 0 [itex]\frac{-221}{82}[/itex]
0 1 0 [itex]\frac{59}{82}[/itex]
0 0 1 [itex]\frac{11}{49}[/itex]
0 0 0 0
So rank(B) = 3 and span(S) = a[1,0,0[itex]\frac{-221}{82}[/itex]] + b[0,1,0,[itex]\frac{59}{82}[/itex]] +c[0,0,1,[itex]\frac{11}{49}[/itex]] + d[0,0,0,0] for a,b,c,d [itex]\in R[/itex]
i.e. span(S) = [a,b,c,D] ; D = [itex]a\frac{-221}{82}[/itex]+[itex]b\frac{59}{82}[/itex] +[itex]c\frac{11}{49}[/itex] for a,b,c,d [itex]\in R[/itex]
So why would it be the case that you cannot form every vector in [itex]R^{4}[/itex] as a linear combination of vectors in S? Is it because your choice of a,b,c determines D, so that you cannot have that same D for other, arbitrary choices of a,b,c (or different values of D for the same values of a,b,c)? How can I make this sharper? How should I think about this in terms of the rank of the matrix of vectors in S?