Solving double integral without integrating

In summary, the conversation discusses how to make the conclusion that the integral of Int Int (2x) dxdy over R = 0 without actually integrating. This can be done by looking at the symmetry of a circle, which is symmetric about the origin. This means that for each possible x value, there is a corresponding -x value, causing the effects of the two points to cancel out. The conversation also mentions that the circle is actually symmetric about (0,1), but a similar conclusion can be drawn to the original post.
  • #1
kasse
384
1
From an example in my book:

Int Int (2x) dxdy over R = 0

(R is the circe x^2+(y-1)^2=1)

How can one make this conclusion without integrating?
 
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  • #2
Look at the symmetry. A circle is "symmetric about the origin": If (x,y) is in the circle then so is (-x, -y). That means that for each possible x value, you have the corresponding -x and so the "effect" of the two points will cancel out.
 
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  • #3
It's actually symmetric about (0,1), but you can draw a similar conclusion to HallsofIvy's post
 
  • #4
Right, sorry about that! If (x. 1+y) is in the circle, so is (-x, 1- y)!
 

Related to Solving double integral without integrating

1. How do you solve a double integral without integrating?

Solving a double integral without integrating involves using alternative methods such as geometric interpretations, change of variables, or symmetry to evaluate the integral.

2. Can you explain the geometric interpretation method for solving double integrals?

The geometric interpretation method involves visualizing the double integral as a volume under a surface in three-dimensional space. This can help to simplify the integral and make it easier to solve.

3. What is the change of variables method for solving double integrals?

The change of variables method involves substituting variables in the original integral to transform it into a simpler form. This can be done by using a transformation matrix or by using polar, cylindrical, or spherical coordinates.

4. When should I use symmetry to solve a double integral?

Symmetry can be used to simplify a double integral when the integrand has symmetry about one or both of the integration variables. This allows you to reduce the integral to a smaller domain and use symmetry properties to evaluate it.

5. Are there any other methods for solving double integrals without integrating?

Yes, there are other methods such as using partial derivatives, Fourier transforms, or Green's theorem. These methods may be more advanced and require knowledge of advanced mathematics, but they can be useful for solving more complicated double integrals.

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