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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 2 D here's at 5 so you're looking at really the distance between negative 2 & 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 got to get I got to go to to the right just to get I got to go to to the right just to get to 0 and I 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 & 4 is 3 and then let's do one more what is a D so a is it 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 for 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