Double integral for loop of rose r=cos2θ

In summary, the conversation discusses finding the range of values for θ and r in a polar curve. The solution is given and it is mentioned that the range for θ is +-∏/4 and for r is 0 <= r <= cos2θ. It is suggested to plot points on the graph to better understand the concept. The conversation concludes with the understanding that the radius of the circle varies according to cos2θ in polar coordinates.
  • #1
mrcleanhands

Homework Statement



attachment.php?attachmentid=58209&stc=1&d=1366915312.jpg


Homework Equations





The Attempt at a Solution


Solution is given.

I don't understand how +-∏/4 is found as a range for θ
Also why is 0 <= r <= cos2θ

r is always r which is defined as cos2θ
 

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  • #2
mrcleanhands said:

Homework Statement



https://docs.google.com/file/d/0BztURiLWDqMyaVplX0tMYUdNNkE/edit?usp=sharing

Homework Equations





The Attempt at a Solution


Solution is given.
Where? I don't see it.

I don't understand how +-∏/4 is found as a range for θ
Did you draw the graph or have one to look at?

Also why is 0 <= r <= cos2θ

r is always r which is defined as cos2θ

That is r on the curve. If you want the area enclosed, r goes from r=0 to r on the curve, no?
 
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  • #3
I see the graph has now appeared. Plot a few points by hand, say for ##\theta = -\frac {\pi}4,\,-\frac {\pi}6,\,0,\,\frac {\pi}6,\,\frac {\pi}4## and see if you don't get that right hand loop.
 
  • #4
Okay I got it. I haven't done much work with polar co-ordinates so I didn't really process that x^2+y^2=r and the circles radius is now going to vary according to cos...

Thanks :)
 

Related to Double integral for loop of rose r=cos2θ

1. What is a double integral for loop of rose r=cos2θ?

A double integral for loop of rose r=cos2θ is a mathematical concept that involves calculating the area under a curve in polar coordinates. In this particular case, the curve is a rose with the equation r=cos2θ, where r represents the distance from the origin and θ represents the angle.

2. How is a double integral for loop of rose r=cos2θ different from a regular double integral?

The main difference between a double integral for loop of rose r=cos2θ and a regular double integral is the use of polar coordinates instead of rectangular coordinates. This means that the limits of integration and the integrand will be expressed in terms of r and θ instead of x and y.

3. What is the purpose of using a for loop in a double integral for loop of rose r=cos2θ?

The for loop is used to iteratively calculate the value of the double integral. It breaks down the area under the curve into smaller, rectangular regions and calculates the sum of their areas. This allows for a more accurate approximation of the double integral.

4. How do you set up the limits of integration for a double integral for loop of rose r=cos2θ?

The limits of integration for a double integral for loop of rose r=cos2θ are determined by the shape and size of the region of interest. In this case, the region is a circle with a radius of 1, so the limits for r would be 0 to 1. The limits for θ would depend on the desired angle of rotation, typically from 0 to 2π.

5. What are some real-world applications of a double integral for loop of rose r=cos2θ?

Double integrals for loop of rose r=cos2θ have various applications in physics and engineering, such as calculating the moment of inertia for irregularly shaped objects, determining the center of mass, and finding the electric field generated by a charged ring. They can also be used in computer graphics to create visual effects such as 3D modeling and ray tracing.

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