Is Every Line Integral Zero with Green's Theorem?

In summary, The line integral along the given positively oriented curve, an ellipse, using Green's Theorem is zero because the double integral in the attempt at a solution is equal to zero. However, this only applies if the integral is on a conservative field. Otherwise, it may not be zero for all cases.
  • #1
EV33
196
0

Homework Statement


Use Green's Theorem to evaluate the line integralalone the given positvely oriented curve.

∫[tex]_{c}[/tex] sin(y)dx+xcos(y)dy, C is the ellipse x2+xy+y2=4



Homework Equations





The Attempt at a Solution


∫∫(cos(y)-cos(y))dA=∫∫0dA

Because this ends up being the double integral of zero, does this just mean my answer is zero?
 
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  • #2
That's right. The line integral around any closed curve will be 0.
 
  • #3
Yup.
 
  • #4
Awesome. Thank you both.
 
  • #5
Correction: The line integral around any closed curve will be 0 ONLY if the integral is on a conservative field. otherwise it won't be zero for all cases.
 
  • #6
gomunkul51 said:
Correction: The line integral around any closed curve will be 0 ONLY if the integral is on a conservative field. otherwise it won't be zero for all cases.

Mmm. Well, sure. F=(sin(y),x*cos(y)) is conservative. So the integral of F.dr is zero around any closed curve. I didn't mean ANY F. Did that really need a 'correction'?
 
  • #7
Dick said:
Mmm. Well, sure. F=(sin(y),x*cos(y)) is conservative. So the integral of F.dr is zero around any closed curve. I didn't mean ANY F. Did that really need a 'correction'?

It's a subtle point, I wanted EV33 to know that :)
It is very easy to make that mistake and think that any close line integral is zero.
 

FAQ: Is Every Line Integral Zero with Green's Theorem?

What is Green's Theorem?

Green's Theorem is a fundamental theorem in mathematics that relates the line integral of a two-dimensional vector field over a closed curve to the double integral of its divergence over the region enclosed by the curve.

How is Green's Theorem used?

Green's Theorem is used to calculate the values of line integrals and double integrals in a more efficient way, as it allows us to switch between the two types of integrals. It is also used in many applications such as fluid dynamics, electromagnetism, and heat transfer.

What is the significance of zero in Green's Theorem?

The significance of zero in Green's Theorem is that it states that the line integral of a conservative vector field over a closed curve is equal to zero. This means that the work done by the vector field in a closed path is zero, indicating that the field is conservative.

How is Green's Theorem related to the concept of a conservative field?

Green's Theorem is closely related to the concept of a conservative field since it states that a vector field is conservative if and only if the line integral of that field over a closed path is equal to zero. This is because conservative fields have a property known as path independence, meaning that the work done by the field is independent of the path taken.

Can Green's Theorem be extended to higher dimensions?

Yes, Green's Theorem can be extended to higher dimensions through the use of the generalization known as the Stokes' Theorem. This theorem relates the integral of a differential form over an oriented manifold to the integral of its exterior derivative over the boundary of the manifold, and it encompasses Green's Theorem as a special case.

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