The formula for calculating the center of mass in the double integral of the postgraduate entrance examination is ∫∫D xdxdy= the abscissa area of the center of gravity × d, ∫∫D ydxdy= the ordinate area of the center of gravity × d.

The centroid of a surface is the geometric center of a cross-sectional figure. Centroid is used for real objects, and centroid is used for abstract geometry. For real objects with uniform density, the centroid and centroid coincide. The centroid of a section with only one axis of symmetry must be on its axis of symmetry, and the specific points on the axis of symmetry need to be calculated and determined.

Extended data:

The center of the cone or pyramid is located on the line segment connecting the vertex and the center of the bottom, and the ratio is 3: 1. If the center is certain, then this center is the fixed point of all its symmetric groups. So symmetry can determine the whole or part of the center, depending on the kind of symmetry. In addition, we can know that if an object has transitive symmetry, its center is uncertain or not inside, because the transitive transformation group has no fixed point.

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