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• facenian
In summary, the inverse function theorem guarantees the existence of a local inverse when ##J(f)\neq 0## at a point in the domain, but it does not necessarily hold for all points in the domain. Additional conditions may be needed to prove the statement that ##J(f)\neq 0## in ##U## for a bijective function of class ##C^m##.

#### facenian

Let ##f:U\subset R^n\rightarrow V\subset R^n## be a biyective function of class ##C^m(m\geq 1)##, ##U## and ##V## are open sets in ##R^n##. I know from the inverse funtion theorem that when ##J(f)\neq 0## in a point of the the domain a local inverse exists, however, given the above conditions I'd like to know if it is true that ##J(f)\neq 0## in U.(kind of a reciprocal of the inverse function theorem)
For instance, if the inverse of a differentiable function is differentiable this would be easy to prove since
$$\frac{\partial(x_1\ldots x_n)}{\partial(y_1\ldots y_n)}\,\frac{\partial(y_1\ldots y_n)}{\partial(x_1\ldots x_n)}=1\neq 0$$
However I don't know whether this is correct or not.

x^3.

member 587159 and FactChecker

It is not necessarily true that ##J(f)\neq 0## in ##U## for a bijective function of class ##C^m##. The inverse function theorem only guarantees the existence of a local inverse when ##J(f)\neq 0## at a point in the domain, but it does not necessarily hold for all points in the domain.

For example, consider the function ##f(x)=x^3##, which is a bijective function of class ##C^m## for any ##m\geq 1##. However, at ##x=0##, we have ##J(f)=0##, so the inverse function theorem does not apply. This means that there may not exist a local inverse at ##x=0##, even though the function is bijective and of class ##C^m##.

Therefore, it is not enough to just have a bijective function of class ##C^m## to guarantee that ##J(f)\neq 0## in ##U##. You would need additional conditions, such as the inverse of a differentiable function being differentiable, to prove this statement.

## What is an inverse function?

An inverse function is a mathematical operation that undoes the original operation. It essentially reverses the input and output of a function.

## How do you find the inverse of a function?

To find the inverse of a function, you can follow these steps:
1. Rewrite the function in terms of x and y instead of the original variables.
2. Swap the x and y variables.
3. Solve for y.
4. Replace y with f^-1(x).
The resulting function is the inverse of the original function.

## What is the domain and range of an inverse function?

The domain of an inverse function is the range of the original function, and the range of an inverse function is the domain of the original function.

## Can any function have an inverse?

No, not all functions have an inverse. For a function to have an inverse, it must be one-to-one, meaning that each input has a unique output. Functions that fail the horizontal line test do not have an inverse.

## What is the notation for inverse functions?

The notation for inverse functions is f^-1(x). It is read as "f inverse of x".