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Homework Statement
Let A be a matrix of size 3x3. Let u and v be vectors in R3, such that Au = v. Prove that the matrix equation Ax=2v has a solution.
Homework Equations
The Attempt at a Solution
Alright, so this is for an intro linear algebra course, so the solution shouldn't be too coomplicated. But what I am confused about, is can i make A equal a matrix, and then solve this problem with actual numbers? Or to prove this, should i be using variables instead?
cause what i did was made:
A =
1 2 3
1 2 3
1 2 3
And then i mad u=
3
2
1
Then i multiplied A by u to get v, and got v=
10
10
10
Then i moved onto proving that Ax=2v has a solution.
So i wrote:
[1 2 3] [x1] = 20
[1 2 3] [x2] = 20
[1 2 3] [x3] = 20
Then i wrote out the matrix:
1 2 3 20
1 2 3 20
1 2 3 20
Passing to RREF i of course got
1 2 3 20
0 0 0 0
0 0 0 0
Which would therefore indicate that with the A and u that i picked, and the other info given that Ax = 2v has a solution because my RREF has 1 basic variable and 2 free variables, with no rows being 0 0 0 ≠ 0.
BUT i just don't know if i should be somehow proving this with variables instead of numbers, cause i see him saying, 'would this be true for a different A and u and v?'
Any help would be appreciated. :) THANKS!