Partial Derivatives, and Differentiable

In summary, the conversation discusses showing the existence of partial derivatives for a function. The person asking the question is wondering if it is sufficient to use the limit definition of a partial derivative to show their existence, and the response confirms that this is indeed possible. It is also noted that a function can have existing partials even if it is not differentiable.
  • #1
EV33
196
0

Homework Statement



I want to show that the partials exist for a certain function.

Homework Equations



My book says that if a function f is differentiable at a point x then the partial derivatives exist.


The Attempt at a Solution



Rather than showing f is differentiable, I am curious if it is sufficient to just use the limit definition of a partial derivative and show that the limit exists?


Thank you for your time.
 
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  • #2
EV33 said:

Homework Statement



I want to show that the partials exist for a certain function.

Homework Equations



My book says that if a function f is differentiable at a point x then the partial derivatives exist.


The Attempt at a Solution



Rather than showing f is differentiable, I am curious if it is sufficient to just use the limit definition of a partial derivative and show that the limit exists?


Thank you for your time.

Yes, to show the partials exists just use the limit definition. A function can fail to be differentiable and still have the partials exist.
 
  • #3
Thank you for the help.
 

1. What is a partial derivative?

A partial derivative is a mathematical concept used in multivariable calculus to measure the rate of change of a function with respect to one of its variables, while holding all other variables constant. It essentially tells us how much a function changes in response to a small change in one of its variables.

2. How is a partial derivative different from a regular derivative?

A regular derivative measures the rate of change of a single-variable function, while a partial derivative measures the rate of change of a multivariable function with respect to one of its variables. This means that a partial derivative takes into account the effects of all other variables on the function, while a regular derivative only considers changes in one variable.

3. What is the purpose of calculating partial derivatives?

Calculating partial derivatives allows us to better understand the behavior of multivariable functions and their relationships to their input variables. It is also a crucial tool in optimization, as it helps us find the minimum or maximum values of a function.

4. Can a function be differentiable but not continuous?

No, a function cannot be differentiable at a point if it is not continuous at that point. Differentiability requires that the function is continuous and has a well-defined tangent line at that point.

5. How do you determine if a function is differentiable?

A function is differentiable if all of its partial derivatives exist at every point in its domain. In other words, all of its tangent lines must be well-defined and have a finite slope at every point. This can be determined through the use of the limit definition of a derivative or by checking if the function satisfies the differentiability conditions (the existence of all partial derivatives and their continuity).

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