What am I doing wrong when solving this Green's theorem problem?

In summary, Green's theorem is a fundamental theorem in vector calculus that relates a line integral around a closed curve to a double integral over the region enclosed by the curve. It is useful for solving problems involving line integrals and double integrals, especially in the context of conservative vector fields. To determine if a vector field is conservative, you can use the test for conservative vector fields, which involves checking if the partial derivatives of the vector field are equal. Common mistakes when using Green's theorem include not ensuring the region is simple and closed, not correctly setting up the double integral, and not paying attention to orientation and potential singularities. If you are having trouble solving a Green's theorem problem, it is important to review the theorem and break the
  • #1
ainster31
158
1

Homework Statement



gihQcn6.png


Homework Equations


The Attempt at a Solution



$$Q=x\quad P=y^2-2y\\\oint_C{Pdx+Qdy}\\=\int_{C1}(y^2-2y)dx+xdy+\int_{C_2}(y^2-2y)dx+xdy\\=\int_{-\pi/2}^{\pi/2}(((sint+1)^2-2(sint+1))(-sint))dt+cost(cost)dt\\=\int_{-\pi/2}^{\pi/2}(2sin^2t+4sint+2)\\=3\pi$$

Correct answer is ##\pi/2##.
 
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  • #2
Everything is fine except going from second to last step from your answer to the following step.
Integral should be of (- (sint)^3 + sint + (cost)^2) dt
This will give you the correct answer.
 

Related to What am I doing wrong when solving this Green's theorem problem?

1. What is Green's theorem and how does it work?

Green's theorem is a fundamental theorem in vector calculus that relates a line integral around a closed curve to a double integral over the region enclosed by the curve. It is a useful tool for solving problems involving line integrals and double integrals, especially in the context of conservative vector fields.

2. How can I determine if the vector field is conservative?

A vector field is conservative if it can be expressed as the gradient of a scalar function. This means that the line integral of the vector field around a closed curve will be equal to the difference in values of the scalar function evaluated at the endpoints of the curve. To determine if a vector field is conservative, you can use the test for conservative vector fields, which involves checking if the partial derivatives of the vector field are equal. If they are, then the vector field is conservative.

3. What are some common mistakes made when using Green's theorem?

One common mistake when using Green's theorem is not ensuring that the region enclosed by the curve is simple and closed. Another mistake is not correctly setting up the double integral, which involves choosing the correct order of integration and limits of integration. It is also important to pay attention to the orientation of the curve and the direction of the vector field. Finally, it is important to check for any potential singularities or discontinuities in the region that could affect the application of Green's theorem.

4. What should I do if I am having trouble solving a Green's theorem problem?

If you are having trouble solving a Green's theorem problem, it is important to first review the theorem and make sure you understand the concept and its application. You can also try breaking down the problem into smaller steps and working through them methodically. It may also be helpful to consult with a classmate or instructor for clarification or assistance.

5. Can Green's theorem be applied to any type of curve or region?

No, Green's theorem can only be applied to simple and closed curves in the plane and regions that are bounded by these curves. It is not applicable to curves that intersect or regions with holes or openings. In these cases, other methods such as Stoke's theorem or the Divergence theorem may be more appropriate.

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