1 00:00:00,273 --> 00:00:07,464 what i want to do with this video is think about the relationship between variables and then think about what the graph of that relationship should look like. 2 00:00:07,464 --> 00:00:13,212 So let's say these two axis, the horizontal axis over here I plot 3 00:00:13,212 --> 00:00:20,065 the price of a product and lets say this vertical axis over here i plot the demand for the product, and 4 00:00:20,065 --> 00:00:24,498 i'm only plotting the first quadrant here because i'm assuming that the price can only be positive and 5 00:00:24,498 --> 00:00:30,320 i'm assuming that the demand can only be positive, that people aren't going to pay someone to take the product 6 00:00:30,320 --> 00:00:37,114 away from them. So let's think about what would happen for the price and demand for most normal products. 7 00:00:37,114 --> 00:00:43,231 So, if the price is low, you would expect that a lot of poeple are willing to buy that thing they're 8 00:00:43,231 --> 00:00:46,652 like "Oh it's a good price, i would like to buy it." 9 00:00:46,652 --> 00:00:51,163 So, if the price is low, then the demand would be high so maybe it would be somplace over here, all the 10 00:00:51,163 --> 00:00:54,697 way that you would have really high demand if the price was zero. 11 00:00:54,697 --> 00:00:58,581 so if the price was low the deamnd would be high. 12 00:00:58,581 --> 00:01:02,331 Now what happens is the price -- so right here the price is low, demand is high, if the price were to 13 00:01:02,331 --> 00:01:06,464 go up a little bit then maybe the demand goes down a little bit, right? 14 00:01:06,464 --> 00:01:09,280 price went up a little bit demand went down a little bit. 15 00:01:09,280 --> 00:01:13,165 if the price went up a little bit more then maybe demand goes down a little bit more. 16 00:01:13,165 --> 00:01:17,849 as the price went up a bunch then demand would go down a bunch and so the line that represents how the 17 00:01:17,849 --> 00:01:28,115 demand relates to price might look something like this, and i'm just going to assume it's 18 00:01:28,115 --> 00:01:33,099 it a line. It might not be a line, it might be a curve. It might look something like that. 19 00:01:33,099 --> 00:01:37,766 Or it might look something like that. But in general is someone were to ask you, 20 00:01:37,766 --> 00:01:43,030 if you saw this magenta curve that as price increases what happens to demand. 21 00:01:43,030 --> 00:01:47,931 You just say "Well look price increases, as price increases what happens to demand?" 22 00:01:47,931 --> 00:01:53,731 Well demand is decreasing. Now let's think about a different scenario. 23 00:01:53,731 --> 00:02:02,951 Let's talk about the demand for real estate. For actual property, and lets say that on this axis 24 00:02:02,951 --> 00:02:08,648 that we plot the population. The population in the area, and this right over here this is 25 00:02:08,648 --> 00:02:17,682 demand for land. So when the population is very low, you can imagine, if the population is 26 00:02:17,682 --> 00:02:23,447 zero there is no one there that would want to buy land. So if the population is very low 27 00:02:23,447 --> 00:02:26,914 the demand is going to be very low. And as population increases, demand should increase. 28 00:02:26,914 --> 00:02:31,280 If the population increases, more people are going to want to buy land. And if the 29 00:02:31,280 --> 00:02:36,564 population goes up a bunch then a lot of people are going to want to buy land. So you'll see a 30 00:02:36,564 --> 00:02:41,364 line that looks something like this. And once again I drew a line, it doesn't have to be a line 31 00:02:41,364 --> 00:02:47,581 it could be a curve of some kind. It could be a curve that looks something like that, or a curve 32 00:02:47,581 --> 00:02:50,397 that looks something like that. We don't know but the general idea is that if someone 33 00:02:50,397 --> 00:02:56,498 showed you a graph that looked like this. And as population increases what happens to demand. 34 00:02:56,498 --> 00:03:00,231 We'll you'd say "Look, this is population increasing, what happens to demand?" Demand 35 00:03:00,231 --> 00:03:07,049 is going up. Where as price increased the demand went down. Here as population is increasing 36 00:03:07,049 --> 00:03:12,180 demand went up. And you can just make that more general with variables. We're talking about 37 00:03:12,180 --> 00:03:18,298 specific cases here. But if I were to plot something like this, if you were to see a graph that 38 00:03:18,298 --> 00:03:26,479 looked like that and this is the variable x and this is the variable y. And someone were to ask you what 39 00:03:26,479 --> 00:03:38,465 happens to y as x increases. Well you take any x that's the y that we have for that x. 40 00:03:38,465 --> 00:03:42,713 And as you increase x, as you move in the positive horizontal directions. As you increase 41 00:03:42,713 --> 00:03:49,850 x what is happening to y? Y is going up. So for this example, as x increases 42 00:03:49,850 --> 00:04:00,098 y is increasing. If we had a graph that looked like this. Let's call that the 43 00:04:00,098 --> 00:04:05,530 a axis and this is the b axis and maybe our graph looked like this. 44 00:04:05,530 --> 00:04:14,281 What happens as A increases? If you pick an A right over here. We're at that A and that B. 45 00:04:14,281 --> 00:04:24,897 As A increases what's happening to B? Well as A increases our B is lower. As A 46 00:04:24,897 --> 00:04:32,931 increases here B is decreasing. So, just wanting to give you a general idea, when X and Y increased 47 00:04:32,931 --> 00:04:39,864 together the line goes from the bottom left to the top right, we would call this an upward sloping line. 48 00:04:39,864 --> 00:04:49,115 We would call this a positive slope. Everytime X is increased Y also increases is upwards sloping. 49 00:04:49,115 --> 00:04:54,857 When our independant variable increases and our dependent variable decreases. 50 00:04:54,857 --> 00:05:05,466 When the independent variable is increasing, then you say it has a downward slope, when you go from the top left to the bottom right.