What is the determinant of a 3x3 matrix?

In summary: Then look up 'properties of determinants'. Then 'row operations'. Then 'what happens to the determinant of a matrix when you multiply a row by a constant'.
  • #1
Panphobia
435
13

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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  • #2
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.
 
  • #3
Which row operations, I am looking in my textbook and it gives no information on this topic.
 
  • #4
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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  • #5
Panphobia said:
Which row operations, I am looking in my textbook and it gives no information on this topic.

Google is your friend.
 
  • #6
Ray Vickson said:
Google is your friend.

Ack! You revealed my secret. Yes, I typed "row operations determinants" into Google.
 
  • #7
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.
 
  • #8
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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  • #9
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'.
 

1. What is a determinant in math?

A determinant is a value that is calculated from a square matrix. It represents the scaling factor of the linear transformation described by the matrix.

2. How is the determinant of a matrix calculated?

The determinant of a matrix is calculated using a specific formula depending on the size of the matrix. For a 2x2 matrix, the formula is (ad - bc), and for a 3x3 matrix, it is (a(ei - fh) - b(di - fg) + c(dh - eg)).

3. What is the purpose of finding the determinant of a matrix?

The determinant of a matrix is used to solve systems of linear equations, determine the invertibility of a matrix, and calculate the area or volume of shapes in geometry.

4. How does the determinant of a matrix affect the properties of the matrix?

The determinant of a matrix affects the properties of the matrix in several ways. For example, if the determinant is 0, the matrix is not invertible. Additionally, the sign of the determinant can determine whether the matrix is orientation-preserving or orientation-reversing.

5. Are there any shortcuts or tricks for calculating determinants?

There are some shortcuts and tricks for calculating determinants, such as using row operations to simplify the matrix or using patterns in the matrix to quickly find the determinant. However, these shortcuts may not always work and it is important to understand the formula for calculating determinants.

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