 This video will show how to find X and Y intercepts on a graph and then use a graph and rise over run to find slope of a line. So we want to give the ordered pair for an X intercept. An X intercept is where it crosses the X axis and that would be this point right here. So if we find the ordered pair, we start at the origin and we go over 2 to the right, so it's a positive 2 and then we don't go up or down off of the X axis so it would be 2, 0. And if we do the Y intercept, this is where it crosses the Y axis, so that would be this point up here. Again, we start at the origin and go left or right, but we don't, so that would be 0. And then we go 1, 2, 3, 4 units up to get there. So it would be 0, 4. Okay, so now let's talk about rise over run. If we start at the Y intercept and then we count how far up or down we go to get down to a cross from this intercept. So I want to get to this point right here, that's a cross from the X intercept. And you always start from the left most point. I'm comparing these two points by two intercepts, so the Y intercept is to the farthest left. And to get to the X intercept, I would have to go down. So I'm going to go down those four. So I went four units, but since I went down, I went in the negative direction. So down here where the rise was four, but it was in the negative direction, so it's actually negative four. Now, the next step says, going from that Y intercept again to the X intercept, we want to be directly above it. So we want to be at this point. It's directly above the X intercept. So we go from the Y intercept and we go over to the right two. So that means that we went a run of two in the positive direction, so it's a positive two. So the slope of the line is the rise over run, and that's equal to negative four over two, which reduces to negative two. Now, I want to remind ourselves what we did. We went two to the right, and that's why it was a positive two, and we went down four, and that's what made a negative four. Alright, so let's talk about some special lines now. We want to look at a point somewhere that is across from the Y axis. So I'm going to get a new color here. Here's my Y intercept, and I'm going to go pick this point over here that happens to be across from it. And we're going to do that same thing. We're going to talk about rise over run. Now, if I draw a line between these two points, I have a horizontal line. Alright, so in a horizontal line, we're trying to figure out what is the slope of this line. So remember, rise says go from the leftmost point, go up or down to your cross from your point. Well, we already are across from our point, so we didn't go up or down at all, so our rise is zero. And then we have to go from our leftmost point again, and count over until we get either to the point or above or below it. And we are going to go one, two, three, four units, in this case, to the right. And again, we went to the right so that makes it a run of four, of positive four. And zero divided by anything would be zero. So this horizontal line has zero slope. Well, what if we have a vertical line? Again, let's start with this Y axis. It's been a really good point for us. And this time I want to go to a point that's directly below it that'll make a vertical line. So why not go to the origin? I'm going to draw my line here. Oops. When I draw a better line there, I get a vertical line. And if I do, again, the rise over run, I start at the Y intercept. And I figure out how far up or down I have to go to get to across from my point or to my point in this case. And I have to go down that four units. We went down four. Remember, the down is the negative part. So the rise is negative four. And then we have to run. Well, to go directly above or below that point, I already am above that other point. So it would be a run of zero. And when you divide by zero, it's undefined. So we would say that a vertical line has no slope. X intercept is where it crosses the X axis. The Y intercept is where it crosses the Y axis. Vertical lines have no slope. Horizontal lines have zero slope. And rise over run is just how far I had to go up and down or left and right from a leftmost point to a rightmost point.