# High School: Geometry

### Similarity, Right Triangles, and Trigonometry G-SRT.1a

a. A dilation takes a line not passing through the center of the dilation to a parallel line, and leaves a line passing through the center unchanged.

A dilation is a type of transformation that changes the size of an image based on a central point. It's most often used to describe how our pupils grow in the darkness or when we look at something we like. Like ice cream. Mmmmm, ice cream.

Students should know that dilation means choosing a point to be the center, and drawing lines that go through the center and a vertex of the object. To make an object that is similar to the original object, they can draw lines that are parallel to the lines of the object. The intersections with the lines that go through the center are then the points of the new similar object.

That way, we can be sure that all the angles and proportions in the new object are the same. The only thing that has changed is the size. That's what being similar is all about, right?