Main content

## Get ready for Geometry

### Course: Get ready for Geometry > Unit 1

Lesson 2: Scale copies- Exploring scale copies
- Explore scale copies
- Identifying corresponding parts of scaled copies
- Corresponding points and sides of scaled shapes
- Corresponding sides and points
- Identifying scale copies
- Identify scale copies
- Identifying scale factor in drawings
- Identify scale factor in scale drawings
- Identifying values in scale copies
- Scale copies

© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice

# Identifying values in scale copies

Sal identifies missing side lengths in scale drawings.

## Want to join the conversation?

- It sounds like he didn't answer the problems and it's really confusing. Someone help please?(20 votes)
- one point which he did not stress and in the meanwhile it was really important is that after recognizing the length of the figures, we should see how much that side of the figure increases to the another side of the other figure. For example; AB has the length of BC in the figure B however the AB side value is 2 and BC in the figure B is 4 we can see that AB is twice smaller than BC and more importantly -- when the question asks the scale factor from figure A to figure B is, you should always consider the numerator as 1 and the denominator as the value of the scale. like 1/3(11 votes)

- Nani?How do I find to multpule figures with just two scale factors?(11 votes)
- nah just see how much the scale of a figure is bigger than another!(5 votes)

- how do you get mastery in one subject?(5 votes)
- You can get mastery on a subject by taking the unit test on the skill.(16 votes)

- I do not know how it is equal to two, he does not explain well.(7 votes)
- Hey kylie! I'd be very happy to assist you in the form of helping you learn what you need to learn, but I first need you to clarify your question.(2 votes)

- I need help i just dont understand(6 votes)
- what
**henry.exe has stopped working**(6 votes) - it's not as hard as the actual questions(6 votes)
- This guy makes this very confusing, any suggestions on hoe to understand this.(5 votes)
- I don't understand this at all(5 votes)
- br e a k f a s t(4 votes)

## Video transcript

- [Instructor] We're told that Figure A is a scale image of Figure B, so that's Figure A, this is Figure B here. The scale that maps Figure A to Figure B is one to two and 1/2. What is the value of X? All right, pause this video and see if you can figure it out. All right, so X is the length of this side right over here on Figure A, and the corresponding side
on Figure B has length five. And so, one way to think about
it is the ratio between X and five should be one to two and a half because that's the scale that goes from Figure A to Figure B. Figure A to Figure B. So, the ratio, let me write this out. The ratio between X and five, so the ratio of X to five, this should be an equivalent ratio as one, one to two and a half. One to two and a half, and
that one is hard to read, let me make it a deeper
blue, there you go. All right, so let's just
think about how to do this. To go from from two and a
half to five, to go that way, you would multiply be two, so to go from one to X, you
would also multiple by two. So, the value of X is equal to two. If these are scaled up, you
multiple this by two and a half, you get to five, so the scale factor is
one to two and a half. Let's do another example. We're told Figure A is a
scale image of Figure B, and we see them both right over here, and once again, we gotta figure out what X is going to be. And they don't give us the scale factor, but we can figure out the scale factor. How do we do that? Well, we can see, when you go from, this side right over here
corresponds to this side. It's the shorter side
that forms a right angle with the base, this is the longer side
that forms a right angle with the base, and so, you could set up some ratios. You can say, look, the
ratio of three to four, you can say the ratio of three to four, we need that blue color, the ratio of three to four is going to be the same thing as
the ratio of X to 7.2. The ratio of X to 7.2, X to 7.2, and so how do we figure
out what X is going to be? Well, how do you go from four to 7.2? What do you have to multiply by? You might wanna get out a calculator or you might be able to
do this in your head. Four 72 is two times 36,
which is two times 18, so four times 18 would be 72 or four times 1.8 would be 7.2, and if you don't feel good
about that mental arithmetic, you could just do the division. Four goes into seven one time, one times four is four, subtract, you get a three, you're gonna have your
decimal right over there, bring down the two, 32, four goes into 32 eight times, eight times four is 32, and we're done. So, to go from four to 7.2, you have to multiply by 1.8 and so, to go from three to X, you also have to multiply by 1.8. And so, X is three times 1.8, what is that going to be? Well, three times 18 is, what? 30, it's 54, so this is going to be 5.4. Let me verify that or show you that. 18 or 1.8 times three, three times eight is 24, three times one is
three, plus two is five, one number behind the decimal
point, 5.4 and we're done.