Identifying scale factor in drawings | Geometry | 7th grade | Khan Academy

So right over here, figure B is a scaled copy of figure A, and 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.

Well, all we have to do is look at corresponding sides and think about how much they have been scaled by. So, for example, this side right over here would correspond to this side right over here on figure B. Over here, it had length two, and over here it has length one, two, three, four, five, six. So it looks like that side has been scaled up by a factor of three.

And so if figure B truly is a scaled copy, then every side should be scaled up by a factor of three, and 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. And 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.