Aim- What is a reflection and how do they impact geometric figures?
Homework- Practice 9-2 #1-9
Please take a polygon (no circles), and a couple pieces of patty paper from the back of the room.
Classwork- Reflections are flips. Geometric figures flip over the line of reflection. Students noticed that during a reflection, the orientation of the vertices changes. They also noticed that pre-image points and their corresponding images are equidistant to the line of reflection.
From yesterday - Today we began a unit on transformations. A transformation is a change in position, shape, or size for a geometric figure. The transformation we learned about today is a translation, which is a slide. On a coordinate plane, a translation lifts a figure and moves it, left-right, up-down. Adding to x-values moves to the right, subtracting x-values moves the figure to the left. Adding to the y-values moves the figure up, subtracting to the y-values moves the figure down. So the notation (x - 3, y + 4) means the figure moves three units to the left and then 4 units up.
The original figure is called a pre-image while the figure after the transformation is called the image.
We also learned that some transformations preserve congruency, meaning the the pre-image and image are congruent to each other. Transformations that preserve congruency are called an isometry.