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# Determining rotations

Videotranscript
- [Voiceover] Use the rotation tool to determine the angle of rotation about the point (2, -3) that will map line segments HE and RO onto the other line segments. So, we wanna rotate HE, this is segment HE, and this is line segment RO, and we wanna rotate it around this point so that they map, so that their images after the rotation map to these two right over here. Let's think about it: which one should map to which? So, it looks like HE should map to this right over here. Well, actually, let me just play around. I can add a rotation. I could add a rotation here, and let's see, I could rotate around. If this point over here is going to, well, we already know we're gonna rotate around the point (2, -3), so let me write that. We're gonna rotate around the point (2, -3), and let's see, if we rotate by 90 degrees, what happens? That was too much. Oh, actually that's too little, because a positive angle right over here, we're going counter-clockwise by 90 degrees, so Point R mapped to this point right over here, Point O mapped to this point over here, but we want it to go even farther. We want it to map to maybe this point over here, so let me increase this. I don't know, let me try 135. All right, it looks like we're almost there. Maybe let's try 140. Press "Enter." That still didn't get us there. Let me see 145. We're getting close, maybe 150. 150, and that looks pretty good. It looks like we have done it. So, if you start with these, the set of points that represent line segments HE and RO, if you rotate them about the point (2, -3) by 150 degrees, and the convention is that that's going to be counter-clockwise, we see that we map, their images are going to be these two lines right over here, and we saw that Point O right over here maps to this point right over here. Point R maps to this point. Point E is going to map to that point, I believe. Yup, that's right, and then Point H is going to map to that point, and obviously all of these points in between, for example, this point right over here that's on the line, that would map to halfway between these two segments right over there, so there we have it. We've done it.