Video of the Day " Triangle Inequalities"

 What makes a triangle actually a triangle? The video demonstrates what defines a triangle.

Transcript
Triangle Inequalities
Hi Welcome to MooMooMath. Today we are going to talk about proportions of a triangles or what happens to the sides that create a triangle. So the best method for me to show you how this works is actually have some straws to show you how triangles work. The first straw is 8 inches long, the second straw is 6 inches long, and then I have some 4's and some 2's. I'm going to draw you some different combinations of triangles. I will show you with the straws which make triangles and which do not.  O if I have the side length of 8 and I pair this with a side length of 4 and a side of 6. Those three pieces can create a triangle. So the bottom one what happens if I replace the side of 4 with a side of only two?  Look what is going to happen. Can I create a triangle? Well guess what, it doesn't reach. They actually are the same length because this side is 8 and this side is 2, and this one is 6, and it's not large enough to reach to the end. So an 8, 6, and 2 don't work. So what happens if I try a 6 and two 2's? OK here is a side of 6 and here is a 2 and here is a 2. Notice how they can't reach each other. So what are the rules for creating triangles? So let's look at the rules. The rules say the two shorter sides have to add up to or be greater than the length of the longer side. So in the first one worked. It was 8, 6, and 4. So 6 and 4 was 10 which is greater than the longer side of 8. So here is another example. If you have a side of 2 and a side of 4 they add up to a number greater than the longest side of 5 so it is a triangle. If this side is 8 and this side is 6 the side of 4 that one works. So let's write the inequality that actually goes with that to represent that it works. So we have a side of 4 inches and a smaller side of 6 inches and they add up to a side greater than 6 inches. Yet the side that was 2 and another of 2 does not add up to a number greater than side that was 6 so this one doesn't work. So the 2 small sides have to add up to be equal or greater than the longer side. Hope this was helpful.

For more on triangle inequalities and an infographic please see MooMooMath/Triangle Inequalities