Matrices and parameters

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  • #1
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Homework Statement


Decide c, so that A(2)X=b(c) where

x=(x,y,z) and b(c)=(1,c,1)
A(2) is calculated from the previous problem:

"Decide the value on the parameter b so that the following system has solutions

(2, 1,-1,b
1, 2, 2, 2b
1,-1,-3, b+1)


Homework Equations





The Attempt at a Solution


Alright, I solved the previous problem that is stated and I got the answer to be b=-1/2
but from that, what do I do? The real question is, what does A(2)x mean? I substitute b for 2?

/Magnus
 

Answers and Replies

  • #2
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6,774
There seems to be some information missing. You mentioned a matrix A(2), but didn't show what it is.

You listed something else, namely
(2, 1,-1,b
1, 2, 2, 2b
1,-1,-3, b+1)
without explaining what it is.

What exactly is the problem you're trying to solve?
 
  • #3
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There seems to be some information missing. You mentioned a matrix A(2), but didn't show what it is.

You listed something else, namely
(2, 1,-1,b
1, 2, 2, 2b
1,-1,-3, b+1)
without explaining what it is.

What exactly is the problem you're trying to solve?


The matrix A(2) is calculated from that one.
"decide the number c so that A(2)x=b(c)
where:
x= (x,y,z) and b(c)=(1,c,1)

A(2) is calculated from the previous example."
The previous example is:
Determine the value on the parameter b so that the following system has solutions:
(2, 1,-1,b
1, 2, 2, 2b
1,-1,-3, b+1)
Where this represents a 3x3 matrix. Any ideas?
 
  • #4
35,028
6,774
By "that one" I assume you mean this 3 x 3 matrix (shown by rows):
{(2 1 -1), (1 2 2), (1 -1 -3)}

The matrix A(2) is calculated from that one.
and
A(2) is calculated from the previous example.

So, to summarize, A(2) is not shown and no description on how to get it is shown, and you don't know what it means.

Not much to go on...
 
  • #5
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By "that one" I assume you mean this 3 x 3 matrix (shown by rows):
{(2 1 -1), (1 2 2), (1 -1 -3)}


and


So, to summarize, A(2) is not shown and no description on how to get it is shown, and you don't know what it means.

Not much to go on...
I'm sorry, it's probably my bad english that confuses you. A(2) is calculated from that 3x3 matrix yes, and I have no idea how to get it either. Do you have any idea?
 
  • #6
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A 3x3 augmented matrix where the bs are the parameters. Just to clarify.
 
  • #7
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No ideas?
 
  • #8
HallsofIvy
Science Advisor
Homework Helper
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"Calculated from it" HOW? "Calculating" it from the previous problem doesn't make sense because the only question in that problem is determing b which is only in the right hand side of the equation, not the coefficient matrix. Do you mean that it is the matrix
[tex]\left[\begin{array}{ccc} 2 & 1 & -1\\ 1 & 2 & 2 \\ 1 & -1 & -3\end{array}\right][/tex]?

If so then the problem is to solve
[tex]\left[\begin{array}{ccc} 2 & 1 & -1\\ 1 & 2 & 2 \\ 1 & -1 & -3\end{array}\right]\left[\begin{array}{c} x \\ y \\ z\end{array}\right]= \left[\begin{array}{ccc} 1 \\ c \\ 1\end{array}\right][/tex]
 
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