how do you find the end point B if they give you the coordinates to A and the midpoint M eg. A(7,-3) M(1,-1) find the endpoint B

First multiply the midpoint by 2 getting you (2,-2) then subtract the midpoint from A for x 7-2 and y -3--2, the difference (5, -1) is B

why are the subtitles Japanese.

Did you try changing the language of the subtitles?

in this video, Sal only explains what to do when you have to subtract. What do you do when you need to add such as: `4x + 7 = 3x + 14` ?

Here you can subtract 7 from both sides to get 4x=3x+7. Then you subtract 3x from both sides of the equations to get x=7.

So, what if the question gave you the length of JK and JL. What would you do than?

Well, in this case, both JK and KL are equal, KL would just be JK. But if they weren't, it's just basic subtraction. You subtract the one side you know (JK) from the total length (JL) and get the remaining side (KL).

What if we have the 2 sublengths but we need to find out IF the middle point is actually the midpoint?

if the three points are in the same line AND the sublengths are equal, it's indeed the midpoint

Why did you subtract -7x+8 from 8x-8 ..?

He knew that 8x-8=7x-6 and he was trying to put all the variables on one side and all the numbers on another side so that he could get x and solve for the total segment

Main content

Algebra basics

Course: Algebra basics > Unit 8

Lesson 1: Equations & geometry

Equation practice with midpoints

Name: Equation practice with midpoints
Uploaded: 2013-07-11T18:09:19Z
Description: Given an information about the distance of a segment's midpoint from its endpoints, Sal forms and solves an equation in order to find the length of the segment.

CCSS.Math:

8.EE.C.7

8.EE.C.7b

Google Classroom

Given an information about the distance of a segment's midpoint from its endpoints, Sal forms and solves an equation in order to find the length of the segment. Created by Sal Khan.

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PCgamerFTW
Posted 9 years ago. Direct link to PCgamerFTW's post “how do you find the end p...”
how do you find the end point B if they give you the coordinates to A and the midpoint M
eg. A(7,-3) M(1,-1) find the endpoint B
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(9 votes)
Answer
- AndrewandJean Feldman
  Posted 9 years ago. Direct link to AndrewandJean Feldman's post “First multiply the midpoi...”
  First multiply the midpoint by 2 getting you (2,-2) then subtract the midpoint from A for x 7-2 and y -3--2, the difference (5, -1) is B
  Comment on AndrewandJean Feldman's post “First multiply the midpoi...”
  (5 votes)
Madison Smith
Posted 8 years ago. Direct link to Madison Smith's post “Around 2:00, 8x - 7x = x?...”
Around
2:00
, 8x - 7x = x? I assume the missing 1 is just a place holder?
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(4 votes)
Answer
Matthew Messer
Posted 7 years ago. Direct link to Matthew Messer's post “why are the subtitles Jap...”
why are the subtitles Japanese.
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(3 votes)
Answer
- Jam0708
  Posted 6 years ago. Direct link to Jam0708's post “Did you try changing the ...”
  Did you try changing the language of the subtitles?
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  (4 votes)
Melia Dezort
Posted 5 years ago. Direct link to Melia Dezort's post “Wait, 8x - 7x would be 1 ...”
Wait, 8x - 7x would be 1 so wouldn't x be 3 instead of 2 ?
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(4 votes)
Answer
iLoveLatias
Posted 7 years ago. Direct link to iLoveLatias's post “in this video, Sal only e...”
in this video, Sal only explains what to do when you have to subtract. What do you do when you need to add such as: 4x + 7 = 3x + 14 ?
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(3 votes)
Answer
- beefstew2002
  Posted 7 years ago. Direct link to beefstew2002's post “Here you can subtract 7 f...”
  Here you can subtract 7 from both sides to get 4x=3x+7. Then you subtract 3x from both sides of the equations to get x=7.
  Comment on beefstew2002's post “Here you can subtract 7 f...”
  (3 votes)
Vampire9697ginger
Posted 10 years ago. Direct link to Vampire9697ginger's post “So, what if the question ...”
So, what if the question gave you the length of JK and JL. What would you do than?
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(3 votes)
Answer
- kylenotanoob
  Posted 10 years ago. Direct link to kylenotanoob's post “Well, in this case, both ...”
  Well, in this case, both JK and KL are equal, KL would just be JK. But if they weren't, it's just basic subtraction. You subtract the one side you know (JK) from the total length (JL) and get the remaining side (KL).
  Button navigates to signup page
  (2 votes)
Peter Ke
Posted 10 years ago. Direct link to Peter Ke's post “Why did you subtract -7x+...”
Why did you subtract -7x+8 from 8x-8 ..?
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(1 vote)
Answer
- Anie Garabedian
  Posted 10 years ago. Direct link to Anie Garabedian's post “He knew that 8x-8=7x-6 an...”
  He knew that 8x-8=7x-6 and he was trying to put all the variables on one side and all the numbers on another side so that he could get x and solve for the total segment
  Button navigates to signup page
  (6 votes)
Kees van Gils
Posted 5 years ago. Direct link to Kees van Gils's post “What if we have the 2 sub...”
What if we have the 2 sublengths but we need to find out IF the middle point is actually the midpoint?
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(2 votes)
Answer
- Osama Al-Bahrani
  Posted 5 years ago. Direct link to Osama Al-Bahrani's post “if the three points are i...”
  if the three points are in the same line AND the sublengths are equal, it's indeed the midpoint
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  (3 votes)
Mikayla Shea Heston
Posted 8 years ago. Direct link to Mikayla Shea Heston's post “How do you change the lan...”
How do you change the language of the captions?
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(3 votes)
Answer
Eric LaRue
Posted 9 years ago. Direct link to Eric LaRue's post “This is my first question...”
This is my first question, and it's completely out of curiosity. Is there a real world situation where someone would be provided with a line segment like the one above bisected equally in half, where someone provides two completely different algebraic values for the line? If someone's measuring a line and then dividing that measurement equally, why not just use the same algebraic measure for both halves of the line?
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(3 votes)
Answer
- Daphne Morales
  Posted 9 years ago. Direct link to Daphne Morales's post “I suppose you can think o...”
  I suppose you can think of it that way, but if you have two people measuring the segment half, then they might come up with two different algebraic measures. then, in that case, this process would come in handy!
  Button navigates to signup page
  (0 votes)

Video transcript

We're told that K is the midpoint of segment, JL. So that tells us that segment JK is going to be congruent to segment KL, that they're going to be the exact same length. And they tell us that segment JK is equal to 8x minus 8. So this distance right over here is equal to 8x minus 8. And then they tell us that segment KL is equal to 7x minus 6, that its length is equal to 7x minus 6. So this length right over here is 7x minus 6. Because K is the midpoint, we know that this length must be equal to this length. So to find JL, we just need to find the whole length. We defined what x is. If we know what x is, then we're going to know what this length is and what this length is. And we could either double one of them or add them together to find the length of the entire segment. So first, let's figure out x. And the best way to figure out x is based on the fact that we know that 8x minus 8 is equal to 7x minus 6. And I just want to reemphasize, how do we know that? Well, they told us that K is the midpoint of JL. This is the midpoint, which tells us that this distance is equal to this distance, or 8x minus 8 is equal to 7x minus 6. Now, to figure out x, we just have to do a little bit of algebra. So let's see what we can do to simplify things. So if we want to get all the x terms on one side-- let's say we're going to get it on the left side-- we could subtract 7x from both sides. So let's do that. Let's subtract 7x from both sides. And if we want to get all of the constant terms on one side, well, let's add 8 to both sides so that we don't have this negative 8 right over here. So let's add 8 to both sides, and let's see what we are left with. On the left-hand side, you don't have an 8 anymore, and 8x minus 7x is just an x. And that's going to be equal to-- on the right-hand side, you don't have any 7x's anymore. And negative 6 plus 8 is just 2. So we get x is equal to 2. But we're not done yet. They didn't say solve for x. They said find JL. So JL is just going to be the sum of JK and KL, or since K is the midpoint, it would just be double JK or double KL. So let's figure out either way. So now we can figure out that JK, the length of segment JK, is equal to 8 times 2 minus 8. We know that x is 2 now. So this is equal to-- well, this is 16 minus 8. This right over here is just equal to 8. And if we wanted to figure out JL, we know that this is halfway, so that this must be 8 as well. And the length of the entire thing, the length of JL must be 16. And if you wanted to spend extra time to make sure that all of the math is consistent, you could put 2 into this right over here. And 7 times 2 is 14 minus 6 is 8. So, once again, you can verify from another direction that this length of segment KL is also 8. 8 plus 8 is 16.

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