 This video is called the Triangle Inequality. When you're given three segments, like on the screen here, you can see three segments of 9, 21 and 20, we want you to figure out could those three be put together to make a triangle, or wouldn't it work? Wouldn't they meet up to make a triangle? Would they just end up making a straight line or not quite be able to touch things like that? So the Triangle Inequality says to have a triangle, the sum of the two smaller sides must be greater or bigger, if that's easier for you to think about, than the longest side. So you'll be asked to determine whether the given measures can be the lengths of the sides of a triangle. You'll be asked to write yes or no and to explain. So basically we just want you to show your work a little bit. So it says the sum of the two smaller sides. So in this example, the two smaller sides are 9 and 20. So when you do 9 plus 20, you get 29. So it says the sum of the two smaller sides has to be bigger or greater than the longest side. Well, the longest side was 21. So is the sum of my smaller sides bigger than 21? Yes, it is. 29 is definitely bigger than 21. So you could say, yes, these three side lengths could be put together to make a triangle. Let's try one more in this video. Again, the instructions say determine whether the given measures can be the lengths of the sides of a triangle. Write yes or no and explain. So again, we pick the smaller two sides. This case, it's the two and the six. So 2 plus 6 equals 8. And we want to know, does the sum of the two smaller sides, is it bigger than 11 or bigger than the biggest side, which in this case is 11? And you can see, no, it's not. 8 is actually smaller than 11. We need this number to be bigger. So you would say no. You're going to see a couple more examples of these in the practice problems later on in your note sheet tonight. So this doesn't quite make sense yet. Don't worry, you'll see more of these and you'll see some more visual aids to help you out. But just keep in mind, if you can make a triangle, you take the smallest two sides and add them up. That needs to be bigger than the third side or the biggest side.