那么，改变一下区域，把这块移到另一侧，我们得到对xdA的双重积分,是原点那的圆面积乘质心的x的坐标。

So, switching the area, moving the area to the other side, I'll get double integral of xdA is the area of origin times the x coordinate of the center of mass.

youdao

那么我们将不会建立带上下限的积分，和积分dx, dy, dy, dx或者在极坐标做线积分，需要说，让我们回忆一下质心的定义。

So, instead of setting up the integral with bounds and integrating dx dy or dy dx or in polar coordinates, I'm just going to say, well, let's remember the definition of a center of mass.

youdao