Measuring Line Segments

What is BD? So when they're just saying BD, they're saying literally the length of segment BD. So they're saying the length from point B to point D. And B is sitting here at negative 2. D here is at 5. So you're looking at, really, the distance between negative 2 and 5. So you literally could just say, well, that's going to be 5-- that's kind of our endpoint-- minus negative 2. So 5 minus negative 2 is the same thing as 5 plus 2 or 7. Another way-- you could literally just count it out. Count out the distance. You go 1, 2-- to get to 0-- 3, 4, 5, 6, 7 to get all the way to 5. Or you could say, look, I've got to go 2 to the right just to get to 0, and I've got to go 5 more to the right to get to D. So that's going to be 7. Let's do a couple more. What is BD again? Well, here we're going from 1 to 4. The distance between 1 and 4 is 3. And then, let's do one more. What is AD? So A is at negative 5. D is all the way at 4. So we're going from negative 5 to 0, which is 5, and then we're going to go 4 more. 5 plus 4 is 9. Or you could say, hey, look, we start at negative 5. We end up at 4. 4 minus negative 5 is the same thing as 4 plus 5, which is 9.