 Here is a quick introduction to geometry. I always thought the rectangle was a fundamental shape and everything else in geometry is derived from them. I don't know, I always use the triangle as a fundamental shape because polygons you get from the area of a triangle, but let me give you sort of my intro that I give to people in regards to geometry where I sort of try to explain to them what the length, area, and volume are. So if you're thinking about geometry and we're talking about Euclidean geometry, flat surface geometry to a certain degree, you can talk about spheres as well, but the formulas change a little bit, right? But let's do this. What do you call this? Ready? What do you call that? What do you call that? That point that really doesn't have any area, it's just a point in space. A point, exactly. We call this a point. Now a point in space, it's not really a dot, it's not a sphere, it's a point, it's a marker. A marker in space has zero dimensions, zero D, right? No dimensions to it, it's just a point in space, right? Now take this point, right? Take this point and stretch it or take your pen and draw on it. What do you call this? What do you call this? A line, exactly. We call this a line. Now a line is one plane, right? So it's 1D, one dimension, right? One D, right? And one dimension means it's got a unit. It's got a unit, okay? Now, if it's got a unit, it all depends what you measure with, right? What your units you like measuring with? It could be, it could be meters, it could be feet, it could be inches, it's length, right? She's laughing. So we could call this the unit would be meters, feet, inches, centimeters, kilometers, miles, yards, whatever you want to call it, right? That's the dimension, it's a line, it's a length, right? Now take that point, right? Draw a line or stretch your point across, right? And then take this line, hopefully it was a straight line, it doesn't look too straight, take this line and stretch it up, right? So pan it up. When you pan it up, in mathematics, what that means is you multiply it, stretch, you got to cover this whole thing going up, right? What do you call this thing? What do you call this thing? There's multiple words for it, right? Surface, surface, it's a surface, right? So if this was link x, this was link x, and this is length y, we have two dimensions that we're going. For us to go figure out what the surface or what the area of this thing is, we take this and multiply it by this, and this is two directions, so it's two-dimensional, right? Two d. And when you have two-dimensional, you're not just meters and feet and inches and centimeters and kilometers and miles, you're meters squared, feet squared, inches squared. You're multiplying a unit with a unit, and if you multiply two identical things, it's just squared, right? So this would be meters squared, feet squared, inches squared, centimeters squared, whatever it is squared, right? Now take this point, stretch it into a line, take your line, pan this line up, you get your surface. Now take the surface and push it either out of the page or into the page, right? Just go push it in, right? So there is our x, there is our y, and this is sort of depth, and we can call this z, if you want. What do you call this? What do you call this? Volume, volume, surface, volume, right? Volume. That's more related to that. Volume, is there another word we could say? Volume, 3d, 3d, it's got three directions, 3d. And if you're going to measure something, you're going to measure things in the same unit, maybe feet, meters, feet, inches, centimeters, kilometers, miles, you multiply the same unit multiple times together, it's cubed, right? So this is meters cubed, feet cubed, inches cubed, centimeters cubed, right? And what type of world do we live in? You take your three dimensions that we exist in right now, right? Add time, okay? Or multiply with time. You get 4d, which is us. We live in a four-dimensional world, right? Three spatial dimension, and we got time, right? For me, this is my intro to geometry, when I first get into teaching someone geometry, and make sure they understand this concept, and then we build from here, right? No matter what grade they're in. I don't know if that would be considered a proof of this, but it's an explanation. I'm pretty sure there's a hardcore mathematical proof to it, okay?