# Implicit function theorem proof question

• Syrus
In summary, the individual is seeking clarification on why it is plausible to consider F as a function of only x and z in equations 8.1-4 and 8.1-5, which are part of the proof of the implicit function theorem for the familiar equation for the implicit solution f(x,y) of F(x,y,z)=c. They also mention their attempt at a solution, specifically the partial derivative fx of the implicit solution f(x,y).
Syrus

## Homework Statement

I understand the proof of the implicit function theorem up to the point in which I have included a photo. This portion serves to prove the familiar equation for the implicit solution f(x,y) of F(x,y,z)=c. My confusion arises between equations 8.1-4 and 8.1-5 when it is stated to "consider F as a function of x and z only." Why is this at all plausible?

## The Attempt at a Solution

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Pardon me, I meant partial derivative fx of the implicit solution f(x,y) of F(x,y,z).

Syrus said:

## Homework Statement

I understand the proof of the implicit function theorem up to the point in which I have included a photo. This portion serves to prove the familiar equation for the implicit solution f(x,y) of F(x,y,z)=c. My confusion arises between equations 8.1-4 and 8.1-5 when it is stated to "consider F as a function of x and z only." Why is this at all plausible?

## The Attempt at a Solution

Your image is much too small and is quite fuzzy---basically unreadable. Please type out the relevant line or two that contains your actual question.

## 1. What is the Implicit Function Theorem?

The Implicit Function Theorem is a fundamental theorem in calculus that states if a multivariate function satisfies certain conditions, then it can be locally represented as an explicit function of one of the variables. This allows us to solve for a variable in terms of the other variables without having to explicitly express it in terms of the other variables.

## 2. What is the proof of the Implicit Function Theorem?

The proof of the Implicit Function Theorem involves using the Inverse Function Theorem and the Chain Rule to show that the derivative of the implicit function can be expressed in terms of the partial derivatives of the original multivariate function. This allows us to solve for the derivative and establish the existence and uniqueness of the implicit function.

## 3. What are the conditions for the Implicit Function Theorem to hold?

The conditions for the Implicit Function Theorem to hold are that the multivariate function must be continuously differentiable, the partial derivative of the multivariate function with respect to the dependent variable must not be zero, and the determinant of the Jacobian matrix (a matrix of all the partial derivatives) must also not be zero at the point of interest.

## 4. How is the Implicit Function Theorem used in real-world applications?

The Implicit Function Theorem is used in various fields, such as economics, physics, and engineering, to solve for unknown variables in equations that cannot be explicitly solved. It is also used to study the behavior of systems by representing them as implicit functions and analyzing their derivatives.

## 5. Are there any limitations to the Implicit Function Theorem?

Yes, there are limitations to the Implicit Function Theorem. It only holds for functions that satisfy the given conditions, and it may not always be possible to find an explicit solution for the dependent variable. Additionally, the implicit function may not be unique in some cases, and the theorem does not provide a method for finding all possible solutions.

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