"Bijective Function: Is It Bijective?

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In summary, a bijective function is a mathematical function that is both one-to-one and onto, meaning that each input has a unique output and every output has a unique input. It is different from other types of functions because it has both of these properties. Bijective functions have many important applications and can be determined by using the horizontal line test. Additionally, all bijective functions are reversible, meaning they have a well-defined inverse function.
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CarmineCortez
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Homework Statement



Is this function bijective ?

f: [0,1] --> [0,1]

f(x) = x if x E [0,1] intersection Q
f(x) = 1-x if x E [0,1]\Q


Homework Equations





The Attempt at a Solution



it is bijective for the rational numbers not sure about the irrationals.
 
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  • #2
Just manually check whether it's 1-1 (consider the different meanings of "f(x)=f(y)") and onto (draw a graph; is there anything in [0,1] that f misses?).
 
  • #3
Why not? If x is irrational and in [0,1] then 1-x is irrational and in [0,1]. The function is pretty easy to invert.
 

1. What is a bijective function?

A bijective function is a type of mathematical function that has both one-to-one and onto properties. This means that for every input, there is exactly one output and every output has a unique input. In simpler terms, a bijective function is a function where each element in the input set is mapped to a different element in the output set, and every element in the output set has a corresponding element in the input set.

2. How is a bijective function different from other types of functions?

A bijective function is different from other types of functions in that it has both one-to-one and onto properties. This means that it is both injective (one-to-one) and surjective (onto). Other types of functions may only have one of these properties, but a bijective function has both.

3. Why is it important for a function to be bijective?

Bijective functions are important in mathematics because they have many useful properties and applications. They are commonly used in cryptography, data encryption, and coding theory. Bijective functions also have a well-defined inverse, making them useful in solving equations and finding solutions to problems.

4. How can you determine if a function is bijective?

To determine if a function is bijective, you can use the horizontal line test. This test involves drawing horizontal lines on a graph of the function. If each horizontal line intersects the graph at only one point, then the function is one-to-one. Additionally, if every element in the output set has a corresponding element in the input set, then the function is onto. If a function passes both of these tests, it is bijective.

5. Are all bijective functions reversible?

Yes, all bijective functions are reversible. This means that they have a well-defined inverse function that maps the output back to the input. For example, if f(x) is a bijective function, its inverse function would be f^-1(x). This allows us to "undo" the function and retrieve the original input from the output.

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