How would you solve this? -2(a+b)+5=x Thanks guys :)

First, you would multiply the parentheses by the outside #. This is using the distributive property. -2(a+b)= -2a-2b The problem now looks like this. -2a-2b+5=x This equation cannot be simplified anymore because the variables of a,b, and x are unknown. Hope this helped. =)

Where do we start when we have the problem A/B=C when we are trying to solve for B

A good way to start would be to get the B "on top" of a fraction, rather than on the bottom. In this case, you can do that by multiplying both sides of the equation by B. This gives you A = BC. Now we need to get rid of the C which is currently on the same side of the equation as B. We can do this by dividing both sides of the equation by C. This gives you A/C = B. And so we have solved for B: we have B = A/C.

Wouldn't the 2 cancel with 2w?

I was going to ask the same thing but I realized that doing so will effect the outcome of P. Doing this will leave P alone. Just like Andrew said, p/2 -w would be the answer.

is there such a video called "What is a variable?"

Yes, there is! In fact, one right here in the website under Algebra I. Just use the search bar and type: "What is a variable." You should be able to find it.

How about if you have a word problem like, "A train makes a trip at 65 mi/h. A plane traveling 130 mi/h makes the same trip in 3 fewer hours. Write and solve an equation to find the distance of the trip." I have this word problem for math homework and I tried solving it with the equation "65mi/h=130mi/h-3" but for some reason I keep on getting the wrong answer. Any help with this problem would be greatly appreciated! Thanks in advance! :)

The key phrase is "makes the same trip". This means both the car and the plane covered the same distance. So, your equation needs to be based upon: `distance of car = distance of plane` Distance is calculated as Rate * Time. You were given the rates: car = 65mph; plane = 130mph. For time, you can use: h=car's time and h-3=plane's time. Thus... Car's distance = 65*h Plane's distance = 130(h-3). The equation becomes:`65h = 130(h-3)` Once you solve for "h", you can find the distance by doing 65*h. Hope this helps.

what if the only coefficient is 1 and all the other #s on the left hand side are variables but on the right side it's like 67 + 93

If the variables were the same variable, add them and 67 + 93, for example: 67 + 93 = 2x + 8x Add like terms. 160 = 10x Isolate x, divide both sides by 10. 16 = x If the variables are different, it depends which variable you were solving for. Say you were solving for x. 67 + 93 = 4x + 3y Add like terms. 160 = 4x + 3y Subtract 3y by both sides. 160 - 3y = 4x Divide both sides by 4. 40 - 3y/4 = x

Main content

Course: Algebra (all content) > Unit 2

Lesson 12: Old school equations with Sal

Solving an equation for a variable

Name: Solving an equation for a variable
Uploaded: 2011-06-21T23:30:09Z
Description: The perimeter of a rectangle is equal to 2 times the length plus 2 times the width. We can solve for the length by isolating it on one side of the equation. We do this by subtracting 2 times the width from both sides, and then dividing both sides by 2. This gives us the formula for the length.

Google Classroom

The perimeter of a rectangle is equal to 2 times the length plus 2 times the width. We can solve for the length by isolating it on one side of the equation. We do this by subtracting 2 times the width from both sides, and then dividing both sides by 2. This gives us the formula for the length. Created by Sal Khan and Monterey Institute for Technology and Education.

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dakshin.sooryamoorthy
Posted 12 years ago. Direct link to dakshin.sooryamoorthy's post “How would you solve this?...”
How would you solve this?

-2(a+b)+5=x

Thanks guys :)
Button navigates to signup pageComment on dakshin.sooryamoorthy's post “How would you solve this?...”
(40 votes)
Answer
- 9958432
  Posted 9 years ago. Direct link to 9958432's post “First, you would multiply...”
  First, you would multiply the parentheses by the outside #. This is using the distributive property.
  -2(a+b)= -2a-2b
  The problem now looks like this.
  -2a-2b+5=x
  This equation cannot be simplified anymore because the variables of a,b, and x are unknown. Hope this helped. =)
  Comment on 9958432's post “First, you would multiply...”
  (13 votes)
edgarsantillan59
Posted 12 years ago. Direct link to edgarsantillan59's post “Where do we start when we...”
Where do we start when we have the problem A/B=C when we are trying to solve for B
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(10 votes)
Answer
- Ben Willetts
  Posted 12 years ago. Direct link to Ben Willetts's post “A good way to start would...”
  A good way to start would be to get the B "on top" of a fraction, rather than on the bottom. In this case, you can do that by multiplying both sides of the equation by B. This gives you A = BC.
  
  Now we need to get rid of the C which is currently on the same side of the equation as B. We can do this by dividing both sides of the equation by C. This gives you A/C = B. And so we have solved for B: we have B = A/C.
  Comment on Ben Willetts's post “A good way to start would...”
  (27 votes)
Ashna
Posted 12 years ago. Direct link to Ashna's post “Wouldn't the 2 cancel wit...”
Wouldn't the 2 cancel with 2w?
Button navigates to signup pageComment on Ashna's post “Wouldn't the 2 cancel wit...”
(8 votes)
Answer
- Marshall
  Posted 11 years ago. Direct link to Marshall's post “I was going to ask the sa...”
  I was going to ask the same thing but I realized that doing so will effect the outcome of P.
  Doing this will leave P alone. Just like Andrew said, p/2 -w would be the answer.
  Comment on Marshall's post “I was going to ask the sa...”
  (8 votes)
LOREAL IS A SAVAGE CABBAGE
Posted 9 years ago. Direct link to LOREAL IS A SAVAGE CABBAGE's post “is there such a video cal...”
is there such a video called "What is a variable?"
Button navigates to signup pageComment on LOREAL IS A SAVAGE CABBAGE's post “is there such a video cal...”
(6 votes)
Answer
- Lucas G.
  Posted 9 years ago. Direct link to Lucas G.'s post “Yes, there is! In fact, o...”
  Yes, there is! In fact, one right here in the website under Algebra I. Just use the search bar and type: "What is a variable." You should be able to find it.
  Button navigates to signup page
  (11 votes)
Komal
Posted 6 years ago. Direct link to Komal's post “How about if you have a w...”
How about if you have a word problem like, "A train makes a trip at 65 mi/h. A plane traveling 130 mi/h makes the same trip in 3 fewer hours. Write and solve an equation to find the distance of the trip."
I have this word problem for math homework and I tried solving it with the equation "65mi/h=130mi/h-3" but for some reason I keep on getting the wrong answer. Any help with this problem would be greatly appreciated! Thanks in advance! :)
Button navigates to signup pageButton navigates to signup page
(6 votes)
Answer
- Kim Seidel
  Posted 6 years ago. Direct link to Kim Seidel's post “The key phrase is "makes ...”
  The key phrase is "makes the same trip". This means both the car and the plane covered the same distance. So, your equation needs to be based upon:
  distance of car = distance of plane
  
  Distance is calculated as Rate * Time.
  You were given the rates: car = 65mph; plane = 130mph.
  For time, you can use: h=car's time and h-3=plane's time.
  Thus...
  Car's distance = 65*h
  Plane's distance = 130(h-3).
  
  The equation becomes:65h = 130(h-3)
  
  Once you solve for "h", you can find the distance by doing 65*h.
  
  Hope this helps.
  Button navigates to signup page
  (9 votes)
1 - Δlex DeRuyter
Posted 5 years ago. Direct link to 1 - Δlex DeRuyter's post “how would you 'un'-isolat...”
how would you 'un'-isolate a variable exactly? can i get some help?
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(4 votes)
Answer
- Vaanya
  Posted 4 years ago. Direct link to Vaanya's post “What do you mean by "un"-...”
  What do you mean by "un"-isolating a variable?
  Button navigates to signup page
  (1 vote)
EvilStealthKiller
Posted 9 years ago. Direct link to EvilStealthKiller's post “Am I the only person who ...”
Am I the only person who is getting problems like "− 5p + 7q − 7r + 2 = 2q − 9r − 6" on the problem set for this video which is only covering a single very simple problem?
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(3 votes)
Answer
Tushar Hirey
Posted 2 years ago. Direct link to Tushar Hirey's post “I think the perimeter of ...”
I think the perimeter of a rectangle is P = 2(w+l) and I think it it much easier to use than the other one. Is this true?
Button navigates to signup pageComment on Tushar Hirey's post “I think the perimeter of ...”
(3 votes)
Answer
Asad Morton
Posted 8 years ago. Direct link to Asad Morton's post “what if the only coeffici...”
what if the only coefficient is 1 and all the other #s on the left hand side are variables but on the right side it's like 67 + 93
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(1 vote)
Answer
- maggie zhang
  Posted 8 years ago. Direct link to maggie zhang's post “If the variables were the...”
  If the variables were the same variable, add them and 67 + 93, for example:
  67 + 93 = 2x + 8x
  Add like terms.
  160 = 10x
  Isolate x, divide both sides by 10.
  16 = x
  If the variables are different, it depends which variable you were solving for. Say you were solving for x.
  67 + 93 = 4x + 3y
  Add like terms.
  160 = 4x + 3y
  Subtract 3y by both sides.
  160 - 3y = 4x
  Divide both sides by 4.
  40 - 3y/4 = x
  Button navigates to signup page
  (5 votes)
Tyler Golden
Posted 6 years ago. Direct link to Tyler Golden's post “How would I solve this eq...”
How would I solve this equation?

x + 3y = 9
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(3 votes)
Answer

Video transcript

Solve P equals 2l plus 2w for l. So this right here, this is just the formula for the perimeter of a rectangle. Perimeter is equal to 2 times the length plus 2 times the width. But they just want us to solve this equation right here, solve for l. So let's do that. So we have P is equal to 2 times l plus 2 times w. So we need to solve for l. So let's isolate all of the l terms on one side. And the best way, we could just do that by leaving it here on the right and then getting rid of this 2w. And the best way to get rid of this 2w is to subtract it from the right. But if you're going to subtract it from the right, you also have to subtract it from the left if you want this equality to hold. So you have to also subtract it from the left. And so the left-hand side becomes P minus 2w. And the right-hand side, you get-- this 2w minus 2w cancels out. You just have a 2l. And then if you want to solve for l, you just have to divide both sides of this equation by 2. You just divide both sides of this equation by 2. And we have isolated our l. We get l is equal to P minus 2w over 2. Or if we wanted to write it the other way, you could write l is equal to P minus 2w over 2. And we are done.