Linear Transformations - formula

  • Thread starter notmuch
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  • #1
16
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Hello. I am given the following:

T([1,2,-3]) = [1,0,4,2]
T([3,5,2]) = [-8,3,0,1]
T([-2,-3,-4]) = [0,2,-1,0]

And of course I know that:

T(x) = Ax

and I want to find the matrix A.

So, from the individual equations, I construct:

A[1, 2, -3] = [1, 0, 4, 2] (please forgive, these are actually col. vectors)

I do something similar for the other two, and come up with the equation below. I can solve this equation to obtain (the correct) matrix A, but I can't seem to find an explanation for why it is possible to throw it all together into "combined matrices." Could anyone help? Thanks!

[tex]
A\begin{pmatrix}
1 & 3 & -2\\
2 & 5 & -3\\
-3 & 2 & -4\end{pmatrix} =
\begin{pmatrix}
1 & -8 & 0\\
0 & 3 & 2\\
4 & 0 & -1\\
2 & 1 & 0\end{pmatrix}
[/tex]
 

Answers and Replies

  • #2
Galileo
Science Advisor
Homework Helper
1,989
6
Because the last matrix is equivalent to the three individual equations. This just follows from matrix multiplication. Schematically, if the v_n's are column vectors, you can write:

[tex]A\left(
\begin{array}{cccc}
\vert & \vert & \vert & \vdots \\
v_1 & v_2 & v_3 & \vdots \\
\vert & \vert & \vert & \vdots \\
\end{array}\right)=\left(
\begin{array}{cccc}
\vert & \vert & \vert & \vdots \\
Av_1 & Av_2 & Av_3 & \vdots \\
\vert & \vert & \vert & \vdots \\
\end{array}\right)[/tex]
 
  • #3
16
0
Got it. Thanks a lot!
 
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