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### Course: Geometry (FL B.E.S.T.)>Unit 9

Lesson 4: 2D vs. 3D objects

# Dilating in 3D

The cross sections of 3D shapes are dilations of the original shape, centered at a specific point. The scale factor of the dilation depends on the height of the cross-section or the distance from the point on the base.  Created by Sal Khan.

## Want to join the conversation?

• Would the dilations and cross sections look the same if you put the 3D pyramid on a coordinate plane?
• How can you put a 3D object such as a pyramid on a coordinate plane which is 2 dimensional? You could put it within a 3D space on an x-y-z coordinate system, but not a coordinate plane.
• Would it look the same if it was a 3D pyramid?
• I'm sorry, but a pyramid is always 3D, so your question makes no sense.
• why does it keep asking for more questions
• هل يمكن لأي شخص أن يشرح لي هذا في فترة أسبوعين
• Would the dilations and cross sections look the same if you put the 3D pyramid on a coordinate plane
(1 vote)
• One, you copied @FemiO, two you can't put a 3D object on a coordinate plane.
• How do we know which dilation is a 0.5 or a 0.75?
• Think of the 0.5 dilation being the halfway point between points B and P going down. For the 0.75 dilation you use the same method, but you go further down (obviously). The closer you cut to the base of the pyramid, the bigger the dilation fraction is.
(1 vote)
• Would the dilations and cross sections look the same if you put the 3D pyramid on a coordinate plane?
• How do you show a 3D figure on a 2D coordinate plane?
(1 vote)
• At , why does he write k=0.5? I get that it's a scale factor, but why k?
(1 vote)
• Hello,
I suppose that it had to do with consistency. Since it's a variable, what we call it doesn't quite matter in terms of the problem, as its just a "placeholder." However, much like how we use x and y to represent coordinate values in the coordinate plane, k is a variable that is commonly seen when dealing with scale factor. Therefore, when you see "k," you could assume that the problem has to deal with scale factor, as that is what k is commonly used for throughout mathematics, and interpret the problem as such. At least, that's what I assume.
Hope this helps!