# Reflections

• Mar 12th 2010, 08:44 AM
mark090480
Reflections
If I reflect something via the line, let's say y=-3 only once, is that considered a translation?

I know doing it twice across parallel lines would do that but not sure about once.

Thanks,

-Mark
• Mar 12th 2010, 08:52 AM
masters
Quote:

Originally Posted by mark090480
If I reflect something via the line, let's say y=-3 only once, is that considered a translation?

I know doing it twice across parallel lines would do that but not sure about once.

Thanks,

-Mark

Hi mark090480,

No. A reflection is a transformation, but not a translation.
• Mar 12th 2010, 09:45 AM
mark090480
But isn't a translation simply moving every point a constant distance in a specified direction. How does a reflection do that? Some points are moved a shorter distance than others.
• Mar 12th 2010, 09:54 AM
masters
Quote:

Originally Posted by mark090480
But isn't a translation simply moving every point a constant distance in a specified direction. How does a reflection do that? Some points are moved a shorter distance than others.

See here: Transformation Geometry: Translations, Reflections, and Rotations
• Mar 12th 2010, 10:01 AM
mark090480
Thanks, but I think I knew that information. Then I read something that said a reflection was a translation in my maths book ( I think it said that, lets say). As far as I can see, that link you gave says that they're different too.
• Mar 12th 2010, 10:46 AM
masters
Quote:

Originally Posted by mark090480
Thanks, but I think I knew that information. Then I read something that said a reflection was a translation in my maths book ( I think it said that, lets say). As far as I can see, that link you gave says that they're different too.

You're right mark, I mis-spoke. A reflection is not a translation. It's a transformation.

A translation is a slide.

Sorry. I will edit my original post before someone else thinks I've lost my mind.

Thanks.
• Mar 12th 2010, 10:52 AM
mark090480
OK, thanks, that is good to know, then I understand how it works too ;)
• Mar 12th 2010, 08:56 PM
mathhomework
My method
I am leaning transformations also. This is how I understand translation and reflection.

Translation is a slide, moving without flipping.
Reflection is a flip, moving with flipping.

So, to reflect over one line, one flip, the preimage and image are different.
To reflect over two parallel lines, it is two flips, the preimage and image are the same after two flips.

I know you understand it now. Just want to show my method, cuz I think it is easier to visualize.