zeldaspurpose
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Homework Statement
Homework Equations
The Attempt at a Solution
I need help with the second question, I did the first one correctly. My pre board is on Monday so please help.
Help with Matrices Homework before Monday
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I need help with the second question, I did the first one correctly. My pre board is on Monday so please help.
Gold Member
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If you look at Q.2 you have not copied it correctly. Matrix multiplication does not commute.
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The problem asks you to find the matrix product [tex]\begin{bmatrix}x & 1 \end{bmatrix}\begin{bmatrix} 6 & -3 \\ 4 & 5\end{bmatrix}[/tex]. I have no idea what you found! You used the answer to the previous problem, MX, rather than M, and somehow multiplied x only by the "6x" in "6x- 3" rather than both?
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I don't agree with Hallsoflvy.
##M = \begin{bmatrix} 6 & -3 \\ 4 & 5\end{bmatrix}\ \ \begin{bmatrix}x \\ 1 \end{bmatrix} \ \ =\ \begin{bmatrix} (6x-3) \\ (4x+5)\end{bmatrix} ## as OP said.
##M \neq \begin{bmatrix} 6 & -3 \\ 4 & 5\end{bmatrix}## as Hallsoflvy claims.
Therefore in part b, you are asked to find
##\begin{bmatrix}x & 1 \end{bmatrix} M \ \ =\ \begin{bmatrix}x & 1 \end{bmatrix}\ \begin{bmatrix} (6x-3) \\ (4x+5)\end{bmatrix}##
which is what neither said.
OP's error was to write ##M\ \begin{bmatrix}x & 1 \end{bmatrix} ## instead of ##\begin{bmatrix}x & 1 \end{bmatrix}\ M##
##M = \begin{bmatrix} 6 & -3 \\ 4 & 5\end{bmatrix}\ \ \begin{bmatrix}x \\ 1 \end{bmatrix} \ \ =\ \begin{bmatrix} (6x-3) \\ (4x+5)\end{bmatrix} ## as OP said.
##M \neq \begin{bmatrix} 6 & -3 \\ 4 & 5\end{bmatrix}## as Hallsoflvy claims.
Therefore in part b, you are asked to find
##\begin{bmatrix}x & 1 \end{bmatrix} M \ \ =\ \begin{bmatrix}x & 1 \end{bmatrix}\ \begin{bmatrix} (6x-3) \\ (4x+5)\end{bmatrix}##
which is what neither said.
OP's error was to write ##M\ \begin{bmatrix}x & 1 \end{bmatrix} ## instead of ##\begin{bmatrix}x & 1 \end{bmatrix}\ M##
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Yes, I misread the first line!
zeldaspurpose
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Oh, now I understand! I always have a problem with reading the question properly. Thank you both!
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Just remember, with matrices order is important.
And congratulations on asking the question clearly with a nice uploaded pic. Some questioners go on for a dozen posts or more before you find out what they actually need.
And congratulations on asking the question clearly with a nice uploaded pic. Some questioners go on for a dozen posts or more before you find out what they actually need.