Linear Algebra Theorem Proof

In summary: So if you simplify ##\det\left(\mathbf{BAB^{-1}}\right)##, what do you get?You get:det(BAB^-1)=det(A)
  • #1
RWalden21
3
0

Homework Statement



Let A and B be square matrices, with B invertible. Show that det(BAB^-1) = det(A)


Homework Equations



I think its based off the theorem: If A and B are nxn matrices, then det(AB)= det(A)det(B)

The Attempt at a Solution




I started by simplifying BAB^-1det(A) to just try to get det(A) but I'm just not sure how to do the proof.
 
Last edited:
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  • #2
Right so how you would expand de(BAB-1) ? And how does det(B) relate to det(B-1)?
 
  • #3
I suppose you can expand by det(B)det(A)det(B^-1) but I don't know how det(B) relates to det(B^-1). What I was thinking was by expanding and somehow getting B and B^-1 to = I somehow det(A) would remain
 
  • #4
RWalden21 said:
I suppose you can expand by det(B)det(A)det(B^-1) but I don't know how det(B) relates to det(B^-1). What I was thinking was by expanding and somehow getting B and B^-1 to = I somehow det(A) would remain

Hint: B-1B= I so if you find then the determinant of I should be the same as the determinant of B-1B right?
 
  • #5
is this correct?

det(BAB^-1)= det(B)det(A)det(B^-1)= det(BB^-1)det(A)= det(I)det(A)= det(A)

det(I) = 1
 
  • #6
RWalden21 said:
is this correct?

det(BAB^-1)= det(B)det(A)det(B^-1)= det(BB^-1)det(A)= det(I)det(A)= det(A)

det(I) = 1

Yep, that will work. So now you know that det(B-1) = 1/det(B), which may help you somewhere down the road.
 
  • #7
RWalden21 said:

Homework Statement



Let A and B be square matrices, with B invertible. Show that det(BAB^-1) = det(A)

Homework Equations



I think its based off the theorem: If A and B are nxn matrices, then det(AB)= det(A)det(B)

The Attempt at a Solution

I started by simplifying BAB^-1det(A) to just try to get det(A) but I'm just not sure how to do the proof.

Didn't you realize you've like already done the proof? You know that if ##\mathbf A,\;\mathbf B\in\mathbb R##, then ##\det\mathbf{AB}=\det\mathbf A\det\mathbf B## and ##\det\left(\mathbf{A}^{-1}\right)=\det\left(\mathbf{A}\right)^{-1}##. So if you just simplify ##\det\left(\mathbf{BAB^{-1}}\right)##, what do you get?

Edit: Why is the ##\LaTeX## equation not rendering?
Edit2: Ok, now it renders. I just realized there is an even simpler method though. You could just break up the determinant into three parts and the join two of them and you are done.
 
Last edited:
  • #8
dimension10 said:
Didn't you realize you've like already done the proof? You know that if ##\mathbf A,\;\mathbf B\in\mathbb R##
A and B aren't real numbers; they're matrices.
dimension10 said:
, then ##\det\mathbf{AB}=\det\mathbf A\det\mathbf B## and ##\det\left(\mathbf{A}^{-1}\right)=\det\left(\mathbf{A}\right)^{-1}##. So if you just simplify ##\det\left(\mathbf{BAB^{-1}}\right)##, what do you get?
 
  • #9
Mark44 said:
A and B aren't real numbers; they're matrices.

Sorry, I meant ##\mathbf{A},\;\mathbf{B}\in\mathbb R^{n\times n}##
 

1. What is a Linear Algebra Theorem Proof?

A Linear Algebra Theorem Proof is a mathematical argument or demonstration that shows the validity of a theorem in the field of Linear Algebra. It involves using logical reasoning and mathematical techniques to prove that a statement is true.

2. Why is it important to prove theorems in Linear Algebra?

Proving theorems in Linear Algebra is important because it allows us to establish the truth of mathematical statements and build a solid foundation for further mathematical developments. It also helps us to understand the underlying principles and concepts of Linear Algebra and their applications in various fields.

3. What are the steps involved in a Linear Algebra Theorem Proof?

The steps involved in a Linear Algebra Theorem Proof may vary depending on the specific theorem being proved, but they generally involve understanding the statement of the theorem, defining any necessary terms, stating any given assumptions or known facts, and then using logical reasoning and mathematical techniques to arrive at a proof of the theorem.

4. How do you know when a Linear Algebra Theorem Proof is correct?

A Linear Algebra Theorem Proof is considered correct when it follows the accepted rules of logic and mathematical reasoning, and when it can be replicated and verified by other mathematicians. It is also important for the proof to be clear, concise, and well-structured.

5. What are some common techniques used in Linear Algebra Theorem Proofs?

Some common techniques used in Linear Algebra Theorem Proofs include direct proof, proof by contradiction, mathematical induction, and proof by counterexample. These techniques involve using logical arguments, algebraic manipulations, and properties of vector spaces, matrices, and linear transformations to prove theorems in Linear Algebra.

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