Find homogeneous system of linear equations whose solution space is: V = span((1,-2,4,3),(1,-1,6,4),(3,-8,8,3)).

Kaila Branch

Kaila Branch

Answered question

2022-09-20

Find homogeneous system of linear equations whose solution space is: V = span((1,-2,4,3),(1,-1,6,4),(3,-8,8,3)).
First I found vectors were linearly dependent, so I discarded the third vector to form a new base. Next I figured system will have 2 free variables and if we would use gauss-jordan elimination on matrix of a system we would get this:
[ 1 0 0 1 ]

Answer & Explanation

Rachael Conner

Rachael Conner

Beginner2022-09-21Added 8 answers

Actually the 3 vectors are linearly independent. For example, it is not hard to check that
| 1 2 4 3 1 1 6 4 3 8 8 3 1 0 0 0 | = 32 0
So we expect there will be just one equation. Suppose it is that the vector ( ( w , x , y , z )) must satisfy a w + b x + c y + d z = 0. Then we know that a , b , c , d must satisfy:
(1) a 2 b + 4 c + 3 d = 0,
(2) a b + 6 c + 4 d = 0,
(3) 3 a 8 b + 8 c + 3 d = 0
Taking (2)-(1), we get b + 2 c + d = 0, and taking 2(2)-(1), we get a + 8 c + 5 d = 0. Substituting in (3) gives d = 0. So the only possible equation is essentially 8 w + 2 x y = 0. It is easy to check that the three given points all satisfy it and hence all linear combinations of those points will also satisfy it.

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