Proof of bijection of a function

In summary, the conversation discusses how to show that the inverse of a bijection f = (A,B,F) is a bijection from B to A and that for any element x of A, f^(-1)(f(x))=x. The proof involves showing that the inverse function is a function, an injection, and a surjection. The use of contradiction is also mentioned as a potential proof method.
  • #1
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Homework Statement



Consider a bijection f = (A,B,F)
Show that f^(-1) (inverse of f) is a bijection from B to A and that for any element x of A we have
f^(-1)(f(x))=x

The Attempt at a Solution



For this proof can I use contradiction and the say f^(-1) is not a bijection from B to A or there exists an element x of A that f^(-1)(f(x)) != x

If this is what I am supposed to prove. How would I go about doing it? If not what proof method should I use?
 
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  • #2
To show that ##f^{-1}## is a bijection, you need to show three things:
(1) ##f^{-1}## is a function. This is not necessarily true for a general ##f##. For example, if ##f : \mathbb{R} \rightarrow \mathbb{R}## is defined by ##f(x) = x^2##, and ##y > 0##, then ##f^{-1}(y)## is a set containing two distinct elements: ##\sqrt{y}## and ##-\sqrt{y}##.
(2) ##f^{-1}## is an injection, meaning that if ##f^{-1}(y_1) = f^{-1}(y_2)##, then ##y_1 = y_2##.
(3) ##f^{-1}## is a surjection, meaning that if ##x## is in the codomain of ##f^{-1}##, then ##x = f^{-1}(y)## for some ##y## in the domain of ##f^{-1}##.
 
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  • #3
alright I got it.
 

What is "Proof of bijection of a function"?

Proof of bijection of a function refers to the mathematical process of showing that a function is both one-to-one and onto, meaning that each element in the domain maps to a unique element in the range, and every element in the range has at least one corresponding element in the domain.

Why is proving bijection important in mathematics?

Proving bijection is important in mathematics because it guarantees that the function is invertible, meaning that the inverse function exists. This allows for easier problem solving and mathematical manipulation. Additionally, bijection is often used in proofs and theorems in various branches of mathematics.

How is bijection different from other types of functions?

Bijection is unique compared to other types of functions because it has the added requirement of being both one-to-one and onto. Other types of functions, such as one-to-many or many-to-one, do not have this restriction.

What are some common techniques used to prove bijection?

There are several techniques that can be used to prove bijection, including direct proof, proof by contradiction, and proof by induction. In direct proof, the function is shown to be both injective (one-to-one) and surjective (onto) simultaneously. In proof by contradiction, it is assumed that the function is not bijective and a contradiction is found. In proof by induction, the function is shown to be bijective for a base case, and then it is proven that the function remains bijective for all subsequent cases.

Are there any common misconceptions about bijection?

One common misconception about bijection is that it requires the domain and range of a function to have the same cardinality (number of elements). While this is often true, it is not a requirement for bijection. A function can be bijective even if the cardinality of the domain and range are different. Additionally, bijection does not necessarily imply that the function is continuous or differentiable, as those properties are not related to the one-to-one and onto requirements.

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