>> But at any rate, the positive Y values are to the right and the negative values are to the left. The positive C values are above and the negative values below. And the positive X values are in this direction, and then the negative values out there. Now, we can draw the negative part of it, but I want to emphasize the positive idea right here. Now, in looking at the coordinate system, we can identify an XY plane. The XY plane, that's the plane containing the X axis and the Y axis. And to draw that plane, now, if that X axis is coming right at us, then the XY plane would be a flat surface like this. Now, to illustrate it, we have to draw it somehow. And there's a great drawing in your textbook, once again. But we might draw something like this, you see? And then shade in here to try to see a flat surface. And in a similar way, we could talk about the XZ plane, the plane involving X and Z axes. And that plane would look like this, you see? It would kind of be out like this. And now, it's coming toward us here a little bit, but we can't draw that, you see? We have to kind of draw it in perspective, if we can. And then the YZ plane we can see very clearly because it is the plane of the chalkboard here. So it would be just this plane.