Figure 2:

When f(x, y) is integrable in region D, its integral value has nothing to do with the segmentation method. Two groups of straight lines parallel to the coordinate axis can be selected to segment D. At this time, the area of each small region is δσ=δxδy, so in rectangular coordinate system, the area element dσ=dxdy, so the double integral can be expressed as:

It can be seen that the value of the double integral is determined by the product function and the integral region * * *. The calculation of converting the above double integral into quadratic definite integral is called: converting the double integral into quadratic integral or repeated integral.

Extended data:

The geometric center of a convex object is always in it. The geometric center of a non-convex object may be on the outside, such as the geometric center of a ring or bowl is not on the inside.

The center of gravity of the triangle is connected with three vertices, and the six triangles formed have the same area.

The distance from the vertex to the center of gravity is two-thirds of the center line.

Center of gravity, center of gravity, center of gravity, center of gravity, center of gravity, center of gravity, nine o'clock.

The center of gravity, the heart, the nagel point and four points similar to the center of gravity.

The center of gravity of the triangle is also the center of gravity of the midpoint triangle.

In cartesian coordinate system, if the coordinates of vertices are:

The coordinates of the midpoint are:

The coordinates of the center of gravity in the three-line coordinate are:

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