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Sequences of transformations

Determining whether segment lengths and angle measures are preserved under a given sequence of transformations.

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Video transcript

- [Instructor] In past videos, we've thought about whether segment lengths or angle measures are preserved with a transformation. What we're now gonna think about is what is preserved with a sequence of transformations? And in particular, we're gonna think about angle measure. Angle measure and segment lengths. So if you're transforming some type of a shape. Segment, segment lengths. So let's look at this first example. They say a sequence of transformations is described below. So we first do a translation, then we do a reflection over a horizontal line, PQ, then we do vertical stretch about PQ. What is this going to do? Is this going to preserve angle measures and is this going to preserve segment lengths? Well a translation is a rigid transformation and so that will preserve both angle measures and segment lengths. So after that, angle measures and segment lengths are still going to be the same. A reflection over a horizontal line PQ. Well a reflection is also a rigid transformation and so we will continue to preserve angle measure and segment lengths. Then they say a vertical stretch about PQ. Well let's just think about what a vertical stretch does. So if I have some triangle right over here. If I have some triangle that looks like this. Let's say it's triangle A, B, C. And if you were to do a vertical stretch, what's going to happen? Well let's just imagine that we take these sides and we stretch them out so that we now have A is over here or A prime I should say is over there. Let's say that B prime is now over here. This isn't going to be exact. Well what just happened to my triangle? Well the measure of angle C is for sure going to be different now. And my segment lengths are for sure going to be different now. A prime C prime is going to be different than AC in terms of segment length. So a vertical stretch, if we're talking about a stretch in general, this is going to preserve neither. So neither preserved, neither preserved. So in general, if you're doing rigid transformation after rigid transformation, you're gonna preserve both angles and segment lengths. But if you throw a stretch in there, then all bets are off. You're not going to preserve either of them. Let's do another example. A sequence of transformations is described below. And so they give three transformations. So pause this video and think about whether angle measures, segment lengths, or will either both or neither or only one of them be preserved? Alright so first we have a rotation about a point P. That's a rigid transformation, it would preserve both segment lengths and angle measures. Then you have a translation which is also a rigid transformation and so that would preserve both again. Then we have a rotation about point P. So once again, another rigid transformation. So in this situation, everything is going to be preserved. So both angle measure, angle measure and segment length are going to be preserved in this example. Let's do one more example. So here once again we have a sequence of transformations. And so pause this video again and see if you can figure out whether measures, segment lengths, both or neither are going to be preserved. So the first transformation is a dilation. So a dilation is a nonrigid transformation. So segment lengths not preserved. Segment lengths not preserved. And we've seen this in multiple videos already. But in a dilation, angles are preserved. Angles preserved. So already we've lost our segment lengths but we still got our angles. Then we have a rotation about another point Q. So this is a rigid transformation, it would preserve both but we've already lost our segment lengths. But angles are going to continue to be preserved. And then finally a reflection which is still a rigid transformation and it would preserve both, but once again our segment lengths got lost through the dilation but we will preserve, continue to preserve the angles. So in this series of after these three transformations, the only thing that's going to be preserved are going to be your angles.