Small Confusion with Partial Derivative

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SUMMARY

The discussion focuses on the calculation of partial derivatives for the function u(x,y) = f(x^3 + y^2) + g(x^3 + y^2), where f and g are differentiable functions. The key equation to demonstrate is 2y(∂u/∂x) - 3x²(∂u/∂y) = 0. Participants clarify that the correct approach involves recognizing u as a composite function, leading to the expression ∂u/∂x = (du/dp)(∂p/∂x), where p = x^3 + y^2. The confusion arises from the distinction between total and partial derivatives, but it is confirmed that the use of du is appropriate in this context.

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jegues
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Homework Statement



Let u(x,y) = f(x^3 + y^2) +g(x^3 + y^2) such that f and g are differentiable functions. Show that,

2y\frac{\partial u}{\partial x} - 3x^{2} \frac{\partial u}{\partial y} = 0

Homework Equations





The Attempt at a Solution



The part of confused about is how to break down my partial derivatives.

The first thing I'm going to do is,

\text{Let } p=x^3 + y^2

then,

u = f(p) + g(p)

Now how to I extract,

\frac{\partial u}{\partial x},\frac{\partial u}{\partial y}

from here?

Is it simply,

\frac{\partial u}{\partial x} = \frac{du}{dp} \frac{\partial p}{\partial x}

The part that bothers me is that the du on the top is not a \partial.

Is this correct?
 
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jegues said:

Homework Statement



Let u(x,y) = f(x^3 + y^2) +g(x^3 + y^2) such that f and g are differentiable functions. Show that,

2y\frac{\partial u}{\partial x} - 3x^{2} \frac{\partial u}{\partial y} = 0

Homework Equations





The Attempt at a Solution



The part of confused about is how to break down my partial derivatives.

The first thing I'm going to do is,

\text{Let } p=x^3 + y^2

then,

u = f(p) + g(p)

Now how to I extract,

\frac{\partial u}{\partial x},\frac{\partial u}{\partial y}

from here?

Is it simply,

\frac{\partial u}{\partial x} = \frac{du}{dp} \frac{\partial p}{\partial x}

The part that bothers me is that the du on the top is not a \partial.

Is this correct?

I do believe it is. You're actually dealing with a composite function, which is why that du isn't partial.
 
Char. Limit said:
I do believe it is. You're actually dealing with a composite function, which is why that du isn't partial.

I think I'm confused because it says show that,

2y\frac{\partial u}{\partial x} - 3x^{2} \frac{\partial u}{\partial y} = 0

and in here I see,

\frac{\partial u}{\partial x} = \frac{du}{dp} \frac{\partial p}{\partial x}


Do the two d's cancel out and the two p's cancel out?
 

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