Partial Derivative Homework: Show x\nablaf(x)=pf(x)

In summary, the conversation discusses the concept of homogeneity in functions and provides a proof that if a function is differentiable at a point, then it can be shown that x multiplied by the gradient of the function is equal to p times the function itself. The chain rule is used to calculate the right hand side of the equation.
  • #1
ak123456
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Homework Statement


A function f: R^n--R is homogenous of degree p if f( [tex]\lambda[/tex]x)=[tex]\lambda[/tex]^p f(x) for all [tex]\lambda[/tex][tex]\in[/tex]R and all x[tex]\in[/tex]R^n
show that if f is differentiable at x ,then x[tex]\nabla[/tex]f(x)=pf(x)



Homework Equations





The Attempt at a Solution


set g([tex]\lambda[/tex])=f([tex]\lambda[/tex]x)
find out g'(1)
then how to continue ?
 
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  • #2
any help?
 
  • #3
[tex] g( \lambda _ = f( \lambda x)[/tex]

Then [tex]g'( \lambda ) = \sum_{i=1}^{n} \frac{df}{dx_i} \frac{d( \lambda x}{dx_i}[/tex]

The right hand side is obtained using the chain rule. Try to calculate what the right hand side really is
 
  • #4
Office_Shredder said:
[tex] g( \lambda _ = f( \lambda x)[/tex]

Then [tex]g'( \lambda ) = \sum_{i=1}^{n} \frac{df}{dx_i} \frac{d( \lambda x}{dx_i}[/tex]

The right hand side is obtained using the chain rule. Try to calculate what the right hand side really is

i don't know where is the formula for g' comes from
 
  • #5
Office Shredder told you: it is the chain rule.
 

FAQ: Partial Derivative Homework: Show x\nablaf(x)=pf(x)

What is a partial derivative?

A partial derivative is a mathematical concept in multivariable calculus that measures the rate of change of a function with respect to one of its variables, while holding all other variables constant.

How do I calculate a partial derivative?

To calculate a partial derivative, you first need to identify the variable you want to take the derivative with respect to. Then, treat all other variables as constants and use the rules of derivatives to find the derivative of the function with respect to the chosen variable.

What is the notation for a partial derivative?

The notation for a partial derivative is similar to that of a regular derivative, but with a subscript indicating the variable you are taking the derivative with respect to. For example, ∂f/∂x represents the partial derivative of f with respect to x.

How is a partial derivative different from a regular derivative?

A partial derivative only considers the change in one variable, while holding all other variables constant. A regular derivative considers the change in the entire function with respect to one variable.

Why are partial derivatives important?

Partial derivatives are important in many areas of science and engineering, as they allow us to understand how a function changes when only one variable is changing. They are also used in optimization problems and in the study of functions with multiple variables.

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