 This video is called using ratios to find the side lengths of triangles. It is very similar to the video you just watched where you were using ratios to find angle measures of a triangle. It's just very important to read the directions carefully and make sure you're answering what is being asked. This particular problem says the ratio of the measures of the sides of a triangle is 3 to 4 to 5. Its perimeter is 72 inches and it wants you to find the measure of the sides of the triangle. Now this time it's not appropriate to set your ratio up equal to 180 degrees because it's the angles that add up to 180. Side lengths do not add up to 180 degrees. That's why we were given the perimeter because the side lengths of a triangle will add up to a perimeter. So this time my ratio is 3 to 4 to 5. So I'll have 3x plus 4x plus 5x. Well that will all add up to not 180, but this time will be 72. So when you have a side length problem, you'll add your ratios up to the perimeter. When you have finding an angle measures problem, you'll add your angle measures up to 180. So now let's go ahead and solve this. 3x plus 4x is 7x. 7x plus 5x is 12x. So 12x equals 72. And then when I divide both sides by 12, I get x equals 6. Now be careful. Many of you will be tempted to say, oh, I found x. My problem's done. I can move on. This problem did not ask you to find x and wants the measures of the side lengths. So we have to keep going. Shouldn't be too hard though. My ratios were 3x, 4x, and 5x. So I'll have 3 times 6, 4 times 6, and 5 times 6. All I did was replace the x with 6 because we found it to be 6 earlier. So 3 times 6 is 18, 4 times 6 is 24, 5 times 6 is 30. Does 18 plus 24 plus 30 add up to 72? 3, 4, 5, 6, 7, it sure does. So the answer to this problem would be 18, 24, and 30. That would be the side lengths of my triangle. They told us the perimeter was inches, so technically we should write inches to label our answers. You'll have to ask your teacher how strict they're going to be about labels during this chapter.