Showing A Matrix Property Is True

In summary, the conversation discusses how to prove that (A^n)^{-1} = (A^{-1})^n for an invertible matrix A. The use of induction is suggested, and it is also noted that (AB)^{-1} = B^{-1}A^{-1}. The original poster was having trouble with expanding the left side of the equation and received guidance on how to proceed.
  • #1
Bashyboy
1,421
5

Homework Statement


Let A be an invertible matrix. Show that [itex](A^n)^{-1} = (A^{-1})^n[/itex]


Homework Equations





The Attempt at a Solution


I want to begin on the left side of the equality sign; but I am having a little difficulty on expanding it. I started to--[itex](A^n)^{-1} = AAA...A^{-1}[/itex]--but it just didn't appear correct. Could someone help me?
 
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  • #2
I would be inclined to prove it using "induction". If n= 1, this just says that [itex](A)^{-1}= A^{-1}[/itex]. Now, suppose [itex](A^k)^{-1}= (A^{-1})^k[/itex]. What can you say about [itex](A^{k+1})^{-1}= ((A^k)A)^{-1}[/itex]?

(You will need to prove separately that [itex](AB)^{-1}= B^{-1}A^{-1}[/itex].)

By the way, you have
want to begin on the left side of the equality sign; but I am having a little difficulty on expanding it. I started to--(An)−1 =AAA...A−1 --but it just didn't appear correct. Could someone help me?
.
No, that is not correct. (An)-1 is the multiplicative inverse of An: (An)(An)-1= I.
 

1. How do you show that a matrix property is true?

To show that a matrix property is true, you can use a variety of methods such as direct proof, contradiction, or mathematical induction. These methods involve using logic and mathematical reasoning to demonstrate that the property holds for all possible cases.

2. What is a counterexample in matrix properties?

A counterexample is a specific case or example that disproves a statement or property. In the context of matrix properties, a counterexample shows that the property does not hold for all matrices, and therefore, the statement is not true.

3. Can I use algebraic manipulation to prove a matrix property?

Yes, algebraic manipulation is a common method used to prove matrix properties. By manipulating the elements of the matrix using algebraic operations such as addition, subtraction, and multiplication, you can show that the property holds for all matrices.

4. Why is it important to show that a matrix property is true?

Showing that a matrix property is true is important because it ensures the validity of the property and allows us to use it in future mathematical calculations. It also helps us to better understand the properties and characteristics of matrices.

5. Can I use examples to prove a matrix property?

Yes, providing examples can be a useful way to illustrate the validity of a matrix property. However, it is important to keep in mind that examples alone are not sufficient to prove a property, and you will also need to provide a logical argument to support your claim.

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