1 3 and let S be the set of vectors x E R³ such that Ax e Span { 2 (3) Let A = Find a basis for S 1 which contains the vector -3 1 Solution 1. Note that Ax e Span{} if and only if the first coordinate of Ax is 0, in other words if [1 1 3] x = [0], thus S = nul([1 1 3]). We find a basis for S by solving for the general solution in vector form; here the matrix is already in reduced echelon form, and x2, X3 are free variables; we solve for -x2 – 3x3 -31 xi to get x1 = -x2 3x3; thus the general solution is x = x2 = x2 1 + x3 To find X3 a basis containing note that it is contained in S (since [1 1 3|-3 0) so we can apply the 1 -3 1 procedure for finding a basis of the span of -3] 0 0 0 1 3 1 0 -1 1 1 -3 1 R2+=3R3 1 rearrange 1 3 1 1 1 1 0 0

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Chapter7: Eigenvalues And Eigenvectors
Section7.CM: Cumulative Review
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Can anyone explain why x2 and x3 is a free variable in the third line of the solution?

1
(3) Let A =
and let S be the set of vectors x E R³ such that Ax E Span
Find a basis for S
2 1
which contains the vector
-3
1
{}
Solution 1. Note that Ax e Span
if and only if the first coordinate of Ax is 0, in other words if
[1 1 3] x = [0], thus S = nul([1 1 3]). We find a basis for S by solving for the general solution in
vector form; here the matrix is already in reduced echelon form, and x2, x3 are free variables; we solve for
-x2 – 3x3
xị to get x1 = -x2 – 3x3; thus the general solution is x =
X2
= x2
+ x3
. To find
X3
1
0.
a basis containing -3
note that it is contained in S (since [1 1 3|-3
[0])
so we can apply the
%3D
1
procedure for finding a basis of the
span
of
0 0
3 R*zR2 0 1 3
1 0 1
-1
-3
-1
ㅇ
1
R2**3Rs 0
rearrange
-3
1
1
1
3
1
1
1
Transcribed Image Text:1 (3) Let A = and let S be the set of vectors x E R³ such that Ax E Span Find a basis for S 2 1 which contains the vector -3 1 {} Solution 1. Note that Ax e Span if and only if the first coordinate of Ax is 0, in other words if [1 1 3] x = [0], thus S = nul([1 1 3]). We find a basis for S by solving for the general solution in vector form; here the matrix is already in reduced echelon form, and x2, x3 are free variables; we solve for -x2 – 3x3 xị to get x1 = -x2 – 3x3; thus the general solution is x = X2 = x2 + x3 . To find X3 1 0. a basis containing -3 note that it is contained in S (since [1 1 3|-3 [0]) so we can apply the %3D 1 procedure for finding a basis of the span of 0 0 3 R*zR2 0 1 3 1 0 1 -1 -3 -1 ㅇ 1 R2**3Rs 0 rearrange -3 1 1 1 3 1 1 1
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