Bijectivity

Definition

Bijectivity is a property of a function that describes a one-to-one correspondence between the elements of the domain and the elements of the codomain. In other words, each element in the domain is uniquely paired with one and only one element in the codomain, and vice versa.

5 Must Know Facts For Your Next Test

1. A bijective function is both injective (one-to-one) and surjective (onto).
2. Bijective functions have the property that for every element in the codomain, there is exactly one corresponding element in the domain.
3. Bijective functions can be reversed to create an inverse function, which maps the codomain back to the original domain.
4. Inverse functions preserve the one-to-one correspondence between the domain and codomain of the original function.
5. Bijectivity is an important property for functions in the context of inverse functions, as it ensures the existence and uniqueness of the inverse.

Review Questions

• Explain how the concept of bijectivity is related to the properties of one-to-one (injective) and onto (surjective) functions.
  • A function is bijective if and only if it is both injective (one-to-one) and surjective (onto). This means that each element in the domain is uniquely paired with one and only one element in the codomain, and every element in the codomain is paired with at least one element in the domain. Bijectivity is a key property that ensures the existence and uniqueness of an inverse function, as it establishes the one-to-one correspondence between the domain and codomain of the original function.
• Describe the role of bijectivity in the context of inverse functions.
  • Bijectivity is a crucial property for the existence and uniqueness of an inverse function. If a function is bijective, then it can be reversed to create an inverse function that maps the codomain back to the original domain. The inverse function preserves the one-to-one correspondence between the domain and codomain of the original function. This ensures that for every element in the codomain, there is exactly one corresponding element in the domain, and vice versa. Without bijectivity, the inverse function may not exist or may not be unique.
• Analyze how the concept of bijectivity can be used to determine the properties of a function and its inverse.
  • $$ \text{If a function } f: A \to B \text{ is bijective, then:} \\ \begin{align*} &1. \text{The function } f \text{ is one-to-one (injective)} \\ &2. \text{The function } f \text{ is onto (surjective)} \\ &3. \text{The inverse function } f^{-1}: B \to A \text{ exists and is unique} \\ &4. \text{The inverse function } f^{-1} \text{ is also bijective} \\ &5. \text{The composition of } f \text{ and } f^{-1} \text{ is the identity function on both } A \text{ and } B \end{align*} $$ These properties of bijective functions and their inverses are crucial in understanding the relationships between a function and its inverse, and in determining the characteristics of both functions.

Related terms

Injective Function: A function is injective (one-to-one) if every element in the codomain is paired with at most one element in the domain.

Surjective Function: A function is surjective (onto) if every element in the codomain is paired with at least one element in the domain.

Inverse Function: An inverse function is a function that 'undoes' the original function, reversing the direction of the mapping between the domain and codomain.