now is parallel to the z axis.

It intersects the y axis at negative one and it never intersects the x axis.

And so when we look at this, we have infinity -1 infinity.

And now if we take the reciprocal of that what we get is the 01bar0.

So again, the fact that our intercept is negative we actually

delineate that by putting the bar over tops and when we see a plane

that's written in this way We immediately know that this is the 0 1 bar 0.

And so, our negative sign then is put up at the top and we read it as a bar.

In review, what we can do is, we can take a look at

the plane that I've indicated here and that is a dihedral plane.

That is, it passes through the cube and when we start looking at our axes,

we position the axes at the point in the rear and then, as a result,

this becomes the one, one bar, zero plane.

As we did in the case of the directions where we talked about specific directions

and directions which are all of the same type,

we can do the same thing when we talk about planes.

So, for example, let's describe again all the faces of the cube.

What I've done is to indicate the origin.

Remember, x, y, and z in a right hand way.

And that first visual that we see is the plane 010.

The 01 bar 0 represents the negative and pay attention to the fact that I have

changed the origin with respect to figure on the left and the figure on the right.

I've done that because when I'm looking at a specific plane,

I do not want to have that plane passing through my selected origin.

And now when we look at the plane that is associated with the third figure

what we see is that's going to be the 001 plane, never intersecting X or

Y, but intersect Z at 1.

Now when we talk about the bottom face of that particular cube.

We have to redirect our position with respect to the origin of our coordinate

system and I've moved it to the top.

And now we don't intersect x, y but we do intersect z.

But this time we're talking about intersecting it at negative one.

And when we look at the 100 plane,

the corresponding 1 bar 00 again I have translated the origin.

And we have thus described all the six faces of the cube and

what we have is specific planes, and now what I can do is lump them all together,

and I can talk about the family of planes as written in red.

So I’ve described then the planes that make up the family of 100.

Thank you.