Proving Inverse Function: f(x)=g-1(x)

In summary, the conversation discusses the definition of the inverse function and how to prove it using the given conditions. The definition of the inverse function is clarified and it is determined that the proof is correct with no exceptions.
  • #1
ritwik06
580
0

Homework Statement


The problem is to prove that:
if
f(g(x))=x ... (1)
and
g(f(x))=x ...(2)

then f(x)=g-1(x)


The Attempt at a Solution


Differentiating (1) wrt x
f'(g(x))*g'(x)=1
f'(g(x))=1/g'(x)

As the slopes are reciprocals of each other, hence f(x)=g-1(x)

Is this as simple as it seems? Are there any possible exceptions?
Is there any more explanatory proof?
Please help me.
 
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  • #2
What you're trying to prove is usually what is taken to be the definition of the inverse function!

What definition are you using then?
 
  • #3
quasar987 said:
What you're trying to prove is usually what is taken to be the definition of the inverse function!

What definition are you using then?

The definition that I use is that the inverse function is the one which returns the input (as its output) when provided with the output of the original function.

So, Have I proved it right? Are there no exceptions to it?
 
  • #4
ritwik06 said:
The definition that I use is that the inverse function is the one which returns the input (as its output) when provided with the output of the original function.

This is not the definition of the inverse (it is the definition of the left inverse). Surely you have the definition of the inverse in mathematical symbols somewhere in your book or class notes?
 
  • #5
ritwik06 said:
The definition that I use is that the inverse function is the one which returns the input (as its output) when provided with the output of the original function.

So, Have I proved it right? Are there no exceptions to it?

I agree with quasar that you might want to review your notes or ask your professor for the definition he or she is using.

However, it seems you're not far off the mark. One suitable definition might be that for any functions f and g such that f:A->B, g:B->A, if for each a in A and b in B, f(a) = b and g(b) = a, then g is the inverse of f.
 

Related to Proving Inverse Function: f(x)=g-1(x)

What is an inverse function?

An inverse function is a mathematical concept that represents the reverse operation of a function. It is essentially the "undoing" of a function, where the output of the original function becomes the input of the inverse function and vice versa.

How do you prove that two functions are inverses of each other?

To prove that two functions f(x) and g(x) are inverses of each other, you must show that when the functions are composed, they result in the identity function. This means that when f(g(x)) and g(f(x)) are evaluated, they both equal x. Additionally, you must also show that the domains and ranges of the functions are interchanged, meaning the domain of f becomes the range of g and vice versa.

What is the process for proving an inverse function?

The process for proving an inverse function involves four steps: 1) Show that the composition of the two functions results in the identity function, 2) Prove that the domains and ranges of the functions are interchanged, 3) Solve for the inverse function by switching the x and y variables, and 4) Verify that the inverse function is indeed the inverse by plugging in values and checking that they result in the original input.

Can any function have an inverse?

No, not all functions have an inverse. For a function to have an inverse, it must be a one-to-one function, meaning that each input has only one unique output. If a function is not one-to-one, it is not possible to reverse the operation and obtain a unique input for each output.

What is the notation for an inverse function?

The notation for an inverse function is f-1(x), where f is the original function. This notation represents the inverse function of f(x) and is read as "f inverse of x".

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