Solving 4x4 Determinant - Find a and b

In summary, the conversation discusses finding the determinant of a 4x4 matrix with variables a and b, and setting it equal to zero using row operations. The conversation also mentions rearranging the matrix using row and column swaps and how the determinant is always zero regardless of the values of a and b. There is also mention of a deleted post that caused confusion and the importance of not leaving incorrect information.
  • #1
cnky
1
0
4x4 determinant(from my exam)

a+b-- a--- a--- a
a--- a+b-- a--- a
a---- a-- a+b-- a detA=0
a---- a--- a--- a+b

How do I find a and b?
 
Last edited:
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  • #2
by finding the determinant and setting it equal to zero. do it by row operations
 
  • #3
(note: this is a response to a deleted reply)

How do you rearrange it like that with row and column swaps? (P.S. the determinant of the matrix you created is clearly zero, no matter what a and b are)
 
Last edited:
  • #4
Hurkyl said:
How do you rearrange it like that with row and column swaps? (P.S. the determinant of the matrix you created is clearly zero, no matter what a and b are)

yes you are right
 
  • #5
hurkyl, you have me puzzled as to why the determinant is clearly zero. take b = 1, a = 0 for instance. then the determinant sure looks like 1 to me, since the matrix is then the identity.

therefore the set of (a,b) with det = 0 apparently forms a curve in the complex (a,b) plane.
 
  • #6
i think hurkyl meant the rearranged one in qutzlcoatl's post, not the original one; i had to think about that too.
 
  • #7
oh, the deleted one.
 
  • #8
yes, the now deleted one... at sciencefourms they don't let ordinary users do that for exactly this reason.
 
  • #9
matt grime said:
yes, the now deleted one... at sciencefourms they don't let ordinary users do that for exactly this reason.

sorry about that, i didn't want to leave something that was wrong and further confuse the matter. i leave it up next time.
 

1. What is a 4x4 determinant?

A 4x4 determinant is a mathematical concept used to solve systems of linear equations with four variables. It involves organizing the coefficients of the variables into a square matrix and calculating its determinant.

2. How do you find a 4x4 determinant?

To find a 4x4 determinant, you need to first set up the matrix with the coefficients of the variables. Then, use the rule of Sarrus or the Laplace expansion method to calculate the determinant. This involves multiplying and adding certain elements of the matrix to obtain the final value.

3. What is the purpose of solving a 4x4 determinant?

Solving a 4x4 determinant is useful in various fields of science and engineering, such as physics, chemistry, and economics. It allows for the solution of systems of equations with four variables, which can represent complex relationships between different quantities.

4. Can you solve a 4x4 determinant by hand?

Yes, you can solve a 4x4 determinant by hand using the rule of Sarrus or the Laplace expansion method. However, for larger matrices, it can be time-consuming and prone to errors, so it is more efficient to use a calculator or computer program.

5. How does finding a and b relate to solving a 4x4 determinant?

Finding a and b is part of the process of solving a 4x4 determinant. The values of a and b are usually unknowns in the system of equations represented by the determinant, and solving for them allows for the determination of the entire solution set.

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