Chapter 6: Problem 29
\mathrm{A}=\\{-1,0,1,2\\}, \mathrm{B}=\\{0,1,2\\}\( and \)\mathrm{f}: \mathrm{A} \rightarrow \mathrm{B}\( defined by \)\mathrm{f}(\mathrm{x})=\mathrm{x}^{2}\(, then \)\mathrm{f}$ is (1) only one-one function (2) only onto function (3) bijective (4) not a function
Short Answer
Expert verified
However, our initial analysis was incorrect, as the function f is neither one-one nor onto. The correct answer is:
Function f is not a one-one, onto, or bijective function.
Step by step solution
01
(1) Define one-one function.
A one-one function (also known as an injective function) is a function where each element in the domain (set A) maps to a unique element in the codomain (set B). In other words, if f(x) = f(y), then x=y.
02
(2) Test f for being one-one.
Using the definition of f, f(x) = x^2. We must check if there exists x, y in set A, such that f(x)=f(y) and x≠y. Let x = -1 and y = 1, then f(x) = (-1)^2 = 1 and f(y) = (1)^2 = 1. Since f(-1) = f(1) but -1≠1, the function f is not one-one.
03
(3) Define onto function.
An onto function (also known as a surjective function) is a function where for every element y in the codomain (set B), there exists an element x in the domain (set A) such that f(x)=y.
04
(4) Test f for being onto.
Using the definition of f, for each element in set B, we must determine if there exists an element in set A that maps to it.
1. For y=0, x=0, f(x) = (0)^2 = 0
2. For y=1, x=1 or x=-1, f(x) = (1)^2 = 1 or f(x) = (-1)^2 = 1
3. For y=2, there is no x in set A such that f(x) = x^2 = 2
Since there is no element in the domain (set A) that maps to the element y=2 in the codomain (set B), the function f is not onto.
05
(5) Define bijective function.
A bijective function is a function that is both one-one (injective) and onto (surjective).
06
(6) Test f for being bijective.
Since we have already determined that function f is neither one-one nor onto, it cannot be a bijective function.
07
(7) Define function.
A function is a relation between two sets A and B such that each element of set A has a unique image in set B. In our case, the function is well-defined, as each element in set A maps to a unique element in set B.
08
(8) Conclusion.
Based on our analysis and testing, the correct answer is: Function f is not one-one or onto, therefore the answer is (1) only one-one function.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
One-One Function
A one-one function, also known as an injective function, is a fundamental concept in mathematics. In such a function, every element in the domain has a unique mapping to the codomain.
This means no two different elements in the domain map to the same element in the codomain. This ensures that if \( f(x) = f(y) \), then \( x = y \).
This means no two different elements in the domain map to the same element in the codomain. This ensures that if \( f(x) = f(y) \), then \( x = y \).
- For example, imagine two elements, \( x = 2 \) and \( y = 3 \) in set A. If both map to 4 in set B, then the function is not injective.
- However, if \( x = 2 \) maps to 4 and \( x = 3 \) maps to 5, then it is one-one.
Onto Function
An onto function, or surjective function, is characterized by its thorough coverage of the codomain.
Essentially, every element in the codomain has at least one pre-image in the domain.
This ensures comprehensive mapping.
Essentially, every element in the codomain has at least one pre-image in the domain.
This ensures comprehensive mapping.
- Consider a codomain that has elements 1, 2, and 3.
- An onto function from a domain will map at least one element from the domain to each of these codomain values.
Bijective Function
A bijective function is a perfect marriage between the one-one and onto functions.
It is both injective and surjective, meaning every element in the domain maps uniquely and comprehensively to elements in the codomain.
So, a bijection ensures each element in both sets has a unique counterpart in the other set, establishing a perfect correlation.
It is both injective and surjective, meaning every element in the domain maps uniquely and comprehensively to elements in the codomain.
- Every domain element maps to a unique codomain element (like one-one).
- Every codomain element is mapped to by some domain element (like onto).
So, a bijection ensures each element in both sets has a unique counterpart in the other set, establishing a perfect correlation.
Function Definition
The concept of a function is pivotal in mathematics, representing a relationship between two sets, typically called the domain and codomain.
A function assigns exactly one output (in the codomain) for each input (in the domain).
Understanding this basic rule is essential when analyzing or constructing functions.
A function assigns exactly one output (in the codomain) for each input (in the domain).
- Imagine a vending machine, where pressing a button (domain) gives you a particular snack (codomain).
- Each action should provide one result, ensuring clarity and reliability in the output.
Understanding this basic rule is essential when analyzing or constructing functions.