And, in terms of a graph, they correspond to slicing by a plane that's parallel to one of the coordinate planes, so that we either keep x constant, or keep y constant.
从图像上看，它们对应于,用平行于坐标轴的平面横截图像得到的，过程中保持x或y恒定。
Remember, partial f, partial x was obtained by y That means I am slicing the graph of f by a plane that is parallel to the x, z plane.
要记得，在这里的fx中,是作为常量保持不变的。，looking，at，the，situation，where，y，is，held，constant。,这是我用一个平行于xz坐标系的平面,横截了f，所得到的图形。
Remember that polar coordinates are about replacing x and y as coordinates for a point on a plane by instead r, r and theta,which is the angle measured counterclockwise from the positive x-axis.
极坐标是关于r，θ的,用r，θ代替平面上一点的x，y坐标，是从原点到那一点的距离，，which，is，the，distance，from，the，origin，to，a，point，θ是由x轴逆时针旋转,而得到的夹角。
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