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。
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.
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, 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.
大面积的餐台玉石面，必须竖抬，避免餐台断裂。小面积的玉石面也应竖拿，切忌平面横抬横拿。
The large bowlder surface of dinner table must be uplifted vertically in avoidance of breakage. The small one shall also be held vertically instead of horizontally.
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