Why is it that the constant = 0?

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Homework Help Overview

The discussion revolves around finding a function \( f \) such that \( \mathbf{F} = \nabla f \) for the vector field \( \mathbf{F}(x,y) = \langle x^3 y^4 , x^4 y^3 \rangle \) and evaluating a line integral along a specified curve. The original poster expresses confusion regarding the constant that arises when determining \( f \), specifically why it is stated to be zero in the solution manual.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the process of finding the potential function and the implications of the constant term. There are questions about the differentiation process and the reasoning behind setting the constant to zero. Some participants suggest that if the derivatives match, the constant can be considered zero, while others express confusion about this conclusion.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem and the reasoning behind the constant. Some guidance has been offered regarding the differentiation process and the nature of the potential function, but there is no explicit consensus on the treatment of the constant.

Contextual Notes

There is mention of the problem's requirement to find a single function \( f \), which may influence the decision to drop the constant term. Participants are also grappling with the implications of the constant in the context of the problem.

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Homework Statement



a) Find a function f such that F = ∇f

b) Evaluate the line integral along the given curve

[tex]\mathbf{F}(x,y) = <x^3 y^4 , x^4 y^3>[/tex]

C: [tex]\mathbf{r}(t) = <\sqrt{t}, 1 + t^3>[/tex] where [tex]t \in [0,1][/tex]


My question

I did everything else right, but my solution manual tells me that the constant i get when I find f is 0

Solutions
[PLAIN]http://img156.imageshack.us/img156/5149/unledoy.jpg
 
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You probably differentiated wrong or something similar. All you do is take the derivative of the potential function after you have integrated it in terms of x. Then you see if this matches the y component of your gradient. If they are the same, then the constant is zero. If they are not the same, then you integrate with respect to y.
 
lineintegral1 said:
You probably differentiated wrong or something similar. All you do is take the derivative of the potential function after you have integrated it in terms of x. Then you see if this matches the y component of your gradient. If they are the same, then the constant is zero. If they are not the same, then you integrate with respect to y.

No they said

g'(y) = 0

g(y) = 0y + K

g(y) = K

I don't understand how you can just take K = 0
 
The problem says to "find a function f..."

All such functions are f(x, y) = (1/4)x4y4 + <some constant>

Since they're looking for just one, it's convenient to drop the constant.
 
Mark44 said:
The problem says to "find a function f..."

All such functions are f(x, y) = (1/4)x4y4 + <some constant>

Since they're looking for just one, it's convenient to drop the constant.

What?? What a stupid question (and stupid student i am...)
 

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