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## Geometry (all content)

### Course: Geometry (all content)>Unit 10

Lesson 9: Old transformations videos

# Performing reflections: line (old)

An older video where Sal uses the interactive widget to find the image of a line under a reflection. Created by Sal Khan.

## Video transcript

We're asked to reflect this line across the line y is equal to negative 4. So you have this line right over here, and they actually give us all of these transformation tools right over here where we can Translate, Rotate, Reflect, Dilate, or Undo what we were about to do. So they want us to reflect this line across y is equal to negative 4. So let's get the Reflection tool out. So I clicked reflect and let's make this line be y equals negative 4. So let's see. That would look something y equals negative 4. So we're going to reflect this line across y equals negative 4. So let's reflect it, and there you have it. We reflected it across y equals negative 4. And then they ask us to answer some questions. When a line is reflected, the image created is a line. We know this is true because a reflected image, well, the original image had zero endpoints. These are just two points on the line, they're not endpoints, they're not defining the end of the line. If they were both endpoints it would be a line segment, but this line keeps going in both directions. So we know this is true because a reflected image has zero endpoints, and we got it right.