What is the determinant of a 3x3 matrix?

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Homework Help Overview

The discussion revolves around finding the determinant of a modified 3x3 matrix based on the properties of determinants and row operations. The original matrix has a known determinant of 5, and participants are exploring how changes to the rows affect the determinant.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the implications of multiplying rows by constants and how that affects the determinant. There is an exploration of the properties of determinants and the challenges posed by having multiple unknowns.

Discussion Status

Some participants have suggested looking up properties of determinants related to row operations, while others have shared resources for further exploration. There is an acknowledgment of the relationship between row operations and the determinant, but no consensus has been reached on the final answer.

Contextual Notes

Participants express confusion regarding the lack of information in their textbooks about row operations and determinants, indicating a need for clarification on these concepts.

Panphobia
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Homework Statement


Determinant
|a b c|
|d e f| = 5
|g h i|
What is the determinant of?
|4a 4b 4c|
|3d 3e 3f|
| g h i|

The Attempt at a Solution


So far I got this, a(ei - hf) - b(di - gf) + c(dh - ge) = 5
How would I even go about this, I have 9 unknowns, but only 1 equations?
 
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Panphobia said:

Homework Statement


Determinant
|a b c|
|d e f| = 5
|g h i|
What is the determinant of?
|4a 4b 4c|
|3d 3e 3f|
| g h i|

The Attempt at a Solution


So far I got this, a(ei - hf) - b(di - gf) + c(dh - ge) = 5
How would I even go about this, I have 9 unknowns, but only 1 equations?

Determinants have properties that are related to row operations. Look some of them up. You don't have to explicitly evaluate the determinants.
 
Which row operations, I am looking in my textbook and it gives no information on this topic.
 
Panphobia said:
Which row operations, I am looking in my textbook and it gives no information on this topic.

Ok, try here. http://science.kennesaw.edu/~plaval/math3260/det2.pdf . What happens to the determinant of a matrix when you multiply a row by a constant?
 
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Panphobia said:
Which row operations, I am looking in my textbook and it gives no information on this topic.

Google is your friend.
 
Ray Vickson said:
Google is your friend.

Ack! You revealed my secret. Yes, I typed "row operations determinants" into Google.
 
Ohh, so if I factore out the 3 and the 4 I would get 12 det(A) where A is the first matrix, then 12 det(A) = 60, oh ok thanks. And Ray, I wouldn't know what to google.
 
Panphobia said:
Ohh, so if I factore out the 3 and the 4 I would get 12 det(A) where A is the first matrix, then 12 det(A) = 60, oh ok thanks. And Ray, I wouldn't know what to google.

Actually, I think I just did "determinant properties". It's not an obscure fact about determinants. Probably in your textbook someplace.
 
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Panphobia said:
Ohh, so if I factore out the 3 and the 4 I would get 12 det(A) where A is the first matrix, then 12 det(A) = 60, oh ok thanks. And Ray, I wouldn't know what to google.

You want to know more about determinants, so Google 'determinant'.
 

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