A **dilation** is a transformation that produces an image that is the *same shape* as the original, but is a *different size.*

A dilation used to create an image **larger** than the original is called an **enlargement**.

A dilation used to create an image** smaller** than the original is called a **reduction**.

To describe a dilation we need two things: a scale factor and a center of dilation. The scale

factor tells us how the size of the “new” figure compares to the size of the old one. If the scale

factor is 1, then the two figures will be exactly the same size. If it is less than 1, the new figure

will be similar to the old one, but smaller, and if it is greater than 1, the new figure will still be

similar to the old one, but will be larger.

HOW TO FIND THE SCALE FACTOR

If you are given two shapes and need to find the scale factor, you must know which one was the original and which one is the image or the new shape. Then you need to know the length of corresponding sides and set them up in a ratio like so:

What scale factor was used to dilate rectangle WXYZ to rectangle W’X’Y’Z’?

First, determine which shape is the original and which is the image.

Since the smaller one does not have the “prime” marks (the little apostrophes) it must be the original one and the one with the marks is the image.

So we set up our ratio like the one above using the lengths given.

So the scale factor is 2.