Inverse Function Proof: f and g are Isomorphisms

In summary: This is the main part of the proof.show that every y in the codomain has an x in the domain with y=f(x).This is the second part of the proof.
  • #1
kathrynag
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Homework Statement



If f:x-->y has an inverse function g, then g:y--->x is one to one and onto

Homework Equations





The Attempt at a Solution


Let g be the inverse of f:x--->y
I think this must have something to do with an isomorphism because of one to one and onto.
 
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  • #2
has more to do with the function being bijective which is both one-one and onto (injective and surjective)

just have to work the definitions, one-one means that only one distinct element gets mapped, and onto implies that the entire range has to be mapped, together these conditions guarantee that only one element gets uniquely mapped to another element throughout the domain we are working in.
 
  • #3
Ok, I understand those defintions. My problem is understanding why g has to be bijective.
 
  • #4
Do you know how to prove that a function is bijective?
 
  • #5
show a(x)=a(y) implies x=y
onto, not entirely sure. I know it has something to do with showing entire range is used
 
  • #6
kathrynag said:
onto, not entirely sure. I know it has something to do with showing entire range is used
Not the range, but the codomain, i.e. for every y in the codomain, there is an x in the domain with y = f(x).
 
  • #7
Let g be the inverse of f:y--->x

Then g(a)=g(b)
a=b
Does this prove one to one? For some resaon I think it doesn't.
 
  • #8
There is an intermediate step between "g(a) = g(b)" and "a = b". How would get rid of the g in g(a) to get a?
 
  • #9
I'm blanking on that
 
  • #10
Apply the inverse of g to both sides of the equation.
 
  • #11
so g^(-1)g(a)=g^(-1)g(b)?
 
  • #12
If g is the inverse of f, then what is the inverse of g? Also, what does g^{-1}(g(a)) evaluate to?
 
  • #13
f is the inverse of g?
 
  • #14
That's right. And what about the answer to my second question.
 
  • #15
f(g(a))
 
  • #16
And that simplifies to ...
 
  • #17
a I think
 
  • #18
That's right. Now what is the complete proof that g is one-to-one?
 
  • #19
by showing a=b
 

FAQ: Inverse Function Proof: f and g are Isomorphisms

What is an isomorphism in relation to inverse functions?

An isomorphism is a function that has a one-to-one correspondence with another function. In the context of inverse functions, an isomorphism is a function that can be reversed to obtain the original function.

How do you prove that f and g are isomorphisms?

To prove that f and g are isomorphisms, you need to show that they are both one-to-one and onto functions. This means that for every element in the domain of f, there is a unique element in the domain of g that maps to it, and vice versa.

What does it mean for f and g to be inverses of each other?

If f and g are inverses of each other, it means that applying f followed by g (or vice versa) will result in the identity function. In other words, the compositions of f and g will cancel each other out, leaving the input unchanged.

What is the importance of proving that f and g are isomorphisms?

Proving that f and g are isomorphisms is important because it guarantees that they are bijective functions, which have many useful properties in mathematics. It also allows for the easy manipulation and understanding of functions by being able to reverse their effects.

Can f and g be isomorphisms if they are not one-to-one or onto?

No, f and g must be both one-to-one and onto to be considered isomorphisms. If they are not, then they cannot be reversed to obtain the original function and therefore do not meet the criteria for an isomorphism.

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