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## Reflections

# Determining reflections

CCSS.Math:

## Video transcript

- [Instructor] We're asked to
draw the line of reflection that reflects triangle ABC,
so that's this blue triangle, onto triangle A prime B prime C prime, which is this red
triangle right over here. And they give us a
little line drawing tool in order to draw the line of reflection. So the way I'm gonna think about it is well, when I just eyeball it, it looks like I'm just flipped over some type of a horizontal line here. But let's see if we can actually construct a horizontal line where
it does actually look like the line of reflection. So let's see, C and C prime, how far apart are they from each other? So if we go one, two,
three, four, five, six down. So they are six apart. So let's see if we just put
this three above C prime and three below C, let's see
if this horizontal line works as a line of reflection. So C, or C prime is
definitely the reflection of C across this line. C is exactly three units above it, and C prime is exactly
three units below it. Let's see if it works for A and A prime. A is one, two, three,
four, five units above it. A prime is one, two, three,
four, five units below it. So that's looking good. Now let's just check out B. So B, we can see it's at the
y-coordinate here is seven. This line right over here
is y is equal to one. And so what we would
have here is, let's see, this looks like it's six
units above this line, and B prime is six units below the line. So this indeed works. We've just constructed
the line of reflection that reflects the blue
triangle, triangle ABC, onto triangle A prime B prime C prime.