Measuring Line Segments
At 51-58s the narrator asks 'what is BD again?' but the example from 1 to 4 is CD (the chapter label says CD). The interventions avoid naming this segment.
The check-ins use the correct version. The video is Khan Academy's, unchanged.About this video
The length of a segment like BD is the distance between its endpoints on a number line. The video finds lengths by subtracting the coordinates (larger minus smaller) or by counting the steps, including when one endpoint is negative.
You'll be able to
- find the length of a segment on a number line by subtracting coordinates.
- find a distance by counting steps across zero.
- handle negative coordinates when measuring segments.
Key words
- line segment
- Part of a line between two endpoints.
- length of a segment
- The distance between its two endpoints; writing BD without a bar means this length.
Transcript
- [Instructor] 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 B, point B to point D. And B is sitting here at negative two, D here is at five. So you're looking at really the distance between negative two and five.
So you literally could just say, well, that's gonna be five, that's kind of our endpoint, minus negative two, so five minus negative two is the same thing as five plus two, or seven. Another way, you could literally just count it out. Count out the distance, you go one, two, to get to zero, three, four, five, six, seven, to get all the way to five.
Or you could say, look, I got to get, I got to go two to the right just to get, I got to go two to the right just to get to zero, and I got to go five more to the right to get to D, so that's going to be seven. Let's do a couple more, what is BD again? Well, here we're going from one to four.
The distance between one and four is three. And then let's do one more, what is AD? So A is a negative five, D is all the way at four. So we're going from negative five to zero, which is five, and then we're gonna go four more, five plus four is nine. Or you could say, hey look, we start at negative five, we end up at four, four minus negative five is the same thing as four plus five, which is nine.
Video © Khan Academy, used under CC BY-NC-SA. Watch on Khan Academy. Puzzicle is not affiliated with Khan Academy.