mutiplying matrix

[RachelB]

Mutiplying matrix

1. [-3 5]
[-2
1]

2. [2 -1
-1 1]
[1 1
1 2]

3. [-1
0
1]
[1 -3]

The directions say "Find the product. If it is not defined, state the reason."

 

[pka]

Your questions are of a level that deserves special attention.
So why don’t you learn to post your questions in LaTeX.
Go to the top of this page. Pull down ‘Forum Help’.
There are links to doing TeX.
Then we can read your postings. Otherwise, you may not get a good response.

 

[stapel]

..."Find the product. If it is not defined, state the reason."

You were already given the solution to similar problems. Are you waiting for somebody to give you the answers to all of them, or are you at some point going to be showing what you've done so far...?

Thank you.

Eliz.

 

[RachelB]

That is the problem, someone gave me the answers but didn't explain how to do it so I have no clue how to work these problems still.

 

[stapel]

That is the problem, someone gave me the answers but didn't explain how to do it so I have no clue how to work these problems still.

It's unfortunate that your class and textbook didn't cover this topic. And since your threads neglected to mention that you were seeking instruction (instead expressing satisfaction with "answer-only" replies), naturally this could be confusing. Thank you for posting the above clarification.

It is not reasonably feasible to attempt to teach courses or lessons within this environment. Fortunately, there are many good instructional resources available online. To find lessons you like, try picking through search-engine listings:

. . . . .Google results for "matrix multiplication"

Once you have studied some lessons and learned the basic terms and techniques, please attempt the posted exercises. If you get stuck, please reply showing your steps, and we'll be glad to try to help you get un-stuck.

Thank you.

Eliz.

 

[soroban]

Hello, Rachel!

You've never done one of these before?
. . And no one has shown you how?

Let me guess . . . Your \(\displaystyle \begin{Bmatrix}\text{teacher}\\ \text{textbook} \\ \text{on-line course} \\ \text{all of the above}\end{Bmatrix}\) really sucks . . . right?

I'll get you started on #1.
You'll have to study to learn to do the rest . . .

\(\displaystyle (1)\;\;\begin{bmatrix}-3 & 5\end{bmatrix}\:\begin{bmatrix}-2 \\ \\ \\ 1\end{bmatrix}\)

We always multiply "Row times Column".


Multiply the first term in the Row by the first term in the Column:

. . \(\displaystyle \;\begin{bmatrix} \fbox{-3} & 5\end{bmatrix}\;\begin{bmatrix}\fbox{-2} \\ \\ \\ 1\end{bmatrix} \;\;\Rightarrow\;\;(-3)(-2)\:=\:6\)


Multiply the second term in the Row by the second term in the Column:

. . \(\displaystyle \:\begin{bmatrix}-3 & \fbox{5}\end{bmatrix}\;\begin{bmatrix}-2 \\ \\ \\ \fbox{1}\end{bmatrix}\;\;\Rightarrow\;\;(5)(1) \:=\:5\)


Add these values: \(\displaystyle \:6\,+\,5\:=\:11\)


Therefore: \(\displaystyle \:\begin{bmatrix}-3 & 5\end{bmatrix}\;\begin{bmatrix}2 \\ \\ \\ 1\end{bmatrix} \;= \;11\)