Confirm Invtblty Property of Cont & Smooth Funcs

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In summary, the textbook is discussing the conditions for a function to be invertible and for its inverse to also be continuous or smooth. While continuity or smoothness of the original function does not necessarily imply the same for its inverse, there are theorems that establish this under certain assumptions. However, there are also counterexamples, such as the inverse function theorem, where the derivative of the inverse may not be continuous even if the original function is invertible and continuous.
  • #1
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My textbook always says things like "[...] such that f is invertible, continuous, and f^-1 is continuous also" and " [...] such that g is invertible, smooth, and g^-1 is smooth also"

But doesn't it follow from "f is conitnuous" that "f^-1 is continuous", and same thing for smooth?
 
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  • #2
No. The standard counterexample is the map from [0,2pi) to the circle (the natural one), which is a bijection, and is continuous since, roughly speaking, small changes in x give small changes in f(x). But in the circle, a small change about f(0) gives a very large change in the inverse image, which will suddenly jimp from just above 0 to just below 2pi.

There are theorems that the continuity of f^-1 follows from that of f under certain additional assumptions, like if the domain is compact and the range is Hausdorff, as is the case, for example, with all functions from a closed interval to R, ie, the functions you usually graph.
 
  • #3
Of course it doesn't follow. Exercise, think of lots of counter example (hint, the inveser function theorem. If f is invertible and f'(0)=0, then what about the derivative of the inverse of f at zero?)
 

FAQ: Confirm Invtblty Property of Cont & Smooth Funcs

1. What is the confirmability property of continuous and smooth functions?

The confirmability property of continuous and smooth functions refers to the ability to verify or prove the truthfulness or validity of these types of functions. This means that given a continuous or smooth function, we can use mathematical methods or tools to confirm that it is indeed continuous or smooth.

2. How do you determine if a function is continuous?

To determine if a function is continuous, we need to check three things: 1) the function must be defined at the point in question, 2) the limit of the function must exist at that point, and 3) the limit must be equal to the value of the function at that point. If all three conditions are met, then the function is continuous at that point.

3. What is the difference between a continuous and a smooth function?

A continuous function is one that is defined and has no breaks or jumps in its graph. On the other hand, a smooth function is not only continuous but also has a continuous derivative. This means that the graph of a smooth function is not only continuous, but it also has no sharp turns or corners.

4. Why is the confirmability property important in mathematics and science?

The confirmability property is important because it allows us to trust and rely on the results or solutions obtained from continuous and smooth functions. It ensures that these functions behave as expected and can be used in various mathematical and scientific applications with confidence.

5. Can any function be both continuous and smooth?

No, not all functions can be both continuous and smooth. In order for a function to be smooth, it must have a continuous derivative. This means that the function must be differentiable at every point in its domain. However, there are functions that are continuous but not differentiable at certain points, such as the absolute value function. Therefore, not all functions can have the confirmability property of both continuity and smoothness.

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