If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: 8th grade (Illustrative Mathematics)>Unit 2

Lesson 3: Lesson 7: Similar polygons

# Dilations and properties

What properties of a shape are preserved or not preserved after a dilation?

## Want to join the conversation?

• Where did you get this dilate tool?
• Does anyone use khan anymore? most of these say 2-3 years ago
• I use it sometimes and I am in march 2020 right now!
(well, when some of you view this it may not be march 2020)
• At , what does "prime" mean?
• The word "prime" can mean several things in mathematics. Most commonly, it's either "prime number" or the "prime symbol". Here, the second meaning is used: the prime symbol.
The prime symbol looks like a single quote: '
It is usually used after a letter, like: x' is "x prime". Its general meaning is "a modified version of the preceding letter". So x' is "a modified version of x", or sometimes "a value related to x".

In the video, Sal uses "B prime" or B' to mean the vertex (= point) that corresponds to B, but on the other (blue) figure.
• Why do they show this and they are nothing simular to the actual questions??
• because it makes it more challenging 😵‍💫
• What does it mean for a line to be preserved?
• Preserved means "stay the same over time",
In this video on dilation, it means: does the line stays the same after the dilation. If the new line sit exactly on top of the first line, then yes.
For a line segment to be preserved, the new line segment needs to sit exactly on top of the first one, which also means they need to start at the exact same point and end at the exact same point.
Hope that helps!
• i watched any payed attention to the whole video and it makes no sense
• what part doesn't make sense🤨
• Do dilations preserve perimeter?
• No, the length of any curve, straight or not, is multiplied by the scale factor of the dilation. So if your figure has perimeter, 6, then after a dilation with a scale factor of 1/3, it will have a perimeter of 2, regardless of the original shape.
• wait whats 2+2 again?
• simple
2 + 2 = 5
• How do you know if they are on parallel lines?
• the lines are next to each other... like:
| | or \ \ or / /
they NEVER Intersect.
You know if they are on a parallel line if you visibly see it on the problem.
I hope this helped!