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Course: 7th grade (Illustrative Mathematics)>Unit 1

Lesson 2: Lesson 2: Corresponding parts and scale factors

Identifying scale factor in drawings

Identify the scale factor used to create a scale copy.

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• I'm still a little confused. I have to turn it into a fraction and it said my fraction was wrong so I flipped it and it was still wrong. Does anyone know how to turn it into a fraction correctly?
• Yes, so when you are looking for the ratio between two similar numbers it is very important to look at the order. If they said ratio of A to B you would do 2/6. The easiest mistake to do in these kind of problems is use the wrong length, just because the shapes are similar does not mean you pick and side length, you must pick the one is corresponding. So if I had two right triangles that were similar, when I found the proportion I couldn't use the smallest side of one and the biggest of the other.
• how much could a wood chuck chuck if a wood chuck could chuck wood
• 83% of the forest causing mass genocide of a variety of species.
• I watched this then took the test and got a fifty on it
• maybe you were having trouble on it? if you were having a hard time, you should rewatch the video and retake the test. however, if this was a hate comment, not very nice! im sorry if it wasn't
-token
• Why didn't Sal measure the longest side of the figure but did that to the rest of the other sides?
• Because you haven't learned the pythagorean theorem yet
• how do you find the scale factor if two sides are missing and if the side that you are multiplying is also gone as well?
• my teacher is sooo confusing
• when arent they
• is this the same video in a nutshell
• I get how to do it, but how do I put it in as an answer? Every time I try it says incorrect. (How do you write it out?)
• What if we need to find X one of the sides
• How do you find the scale copy if two sides are missing?

Video transcript

- [Instructor] Right over here, figure b is a scaled copy of figure a. What we want to do is figure out what is the scale factor to go from figure a to figure b? Pause the video and see if you can figure that out. All we have to do is look at corresponding sides and think about how much they have been scaled by. For example, this side right over here would correspond to this side right over here on figure b. And over here, it had length two and over here it has length one, two three, four, five, six. So, it look like that side has been scaled up by a factor of three. If figure b truly is a scaled copy, then every side should be scaled up by a factor of three. We could verify that. We don't have to do it with every side. We're being told that these are scaled copies but we can see that this is the case. For example, this side right over here, corresponds to this base right over here. This has length three. So, if we're scaling up by a factor of three, we should multiply that by three and this should be of length nine. Let's see if that's the case. One, two, three, four, five, six, seven, eight, and nine. So, you can see, we can feel pretty good that figure b is a scaled copy of figure a and that scaling factor is three.