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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.

## Want to join the conversation?

- Is there any transformation you can even do to the line to make it not be a line any more?(7 votes)
- What if it says " Reflection the line across y=x " ?(5 votes)
- that would be a slope of 1 so it would go through the origin and cross at (1,1) (-1,-1)(1 vote)

- I
`m in 8th grade and i tried the practice quizzes but still don`

t get transformations help?(2 votes) - if A(4,-5) then the image after A is reflected over y-3 is?(2 votes)
- If my point was (-3,-5) and I had to reflect across Y =-1 how would I do that(2 votes)
- Not Able To Understand the lessons what does it means by reflect the line across y=-4(2 votes)
- When reflecting a figure over two lines that are intersecting (does not have to be the axis' just two lines in general) why does it always equal a rotation from the original figure?(2 votes)
- You don't get a rotation. If it was really a rotation, then the reflection would be upside down which is not the case.

But, the interesting point is that one 180 rotation is the equivalent of two reflection ( one over the x-axis, and the second over the y-axis and vice versa)

Hope this helps !

And sorry if my answer is wrong or unclear.(1 vote)

- How do you solve this without a reflect tool?(2 votes)
- How I'm I suppose to reflect a certain object or point over, say for example, x=4 without the reflect tool?(2 votes)
- Okay, I know the rule for a point, (a,b), reflected over y = -x changes the point to ( -b, -a). However, is there a rule for reflecting if the value for x is not -1 ? Ex: y = -2x.(2 votes)

## 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.