Find a basis


by ferry2
Tags: basis
ferry2
ferry2 is offline
#1
Nov24-11, 04:09 PM
P: 15
I don't wan't a solution I wan't only instructions how to solve this problem:

Find a basis for the span: [tex]\vec{a_{1}}=(1,\,-1,\,6,\,0),\,\vec{a_{2}}=(3,\,-2,\,1,\,4),\,\vec{a_{3}}=(1,\,-2,\,1,\,-2),\,\vec{a_{4}}=(10,\,1,\,7,\,3)[/tex]
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nucl34rgg
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#2
Nov24-11, 05:22 PM
P: 129
Make a matrix with a1, a2, a3, and a4 in separate rows, with each component of each vector in a separate column. Put it in row reduced echelon form. The nonzero rows of your new matrix are the vectors that form the basis.
ferry2
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#3
Nov25-11, 12:22 PM
P: 15
So under your guidance the row reduced eshelon form of the matrix:

[tex]A=\left( \begin{array}{cccc}1 &-1 & 6 & 0\\ 3 &-2 & 1 & 4\\ 1 &-2 & 1 &-2\\ 10 & 1 & 7 & 3\\ \end{array} \right)[/tex] is [tex]\left( \begin{array}{cccc}1 & 0 & 0 & 0\\ 0 & 1 & 0 & 0\\ 0 & 0 & 1 & 0\\ 0 & 0 & 0 & 1\\ \end{array} \right)[/tex] so the basis are vectors [tex]\vec{e_1}(1,\,0,\,0,\,0),\,\vec{e_2}(0,\,1,\,0,\,0),\,\vec{e_3}(0,\,0,\ ,1,\,0)[/tex] and [tex]\vec{e_4}(0,\,0,\,0,\,1)[/tex] right?

nucl34rgg
nucl34rgg is offline
#4
Nov25-11, 01:02 PM
P: 129

Find a basis


yeah that's what I got
ferry2
ferry2 is offline
#5
Nov25-11, 01:03 PM
P: 15
Thanks a lot for the tips :).
HallsofIvy
HallsofIvy is offline
#6
Nov26-11, 12:39 PM
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Which says that the span of those four vectors is, in fact, all of [itex]R^4[/itex].
marschmellow
marschmellow is offline
#7
Nov26-11, 04:29 PM
P: 49
Because the span of those vectors is all of R^4, both the 4 standard R^4 basis vectors and the column vectors of your matrix form a basis. What's more interesting is the case when the column vectors do not span the entire space. Then you take the column vectors from your matrix that correspond to the columns with pivots in reduced form, and those form a basis for the column space.


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