Warm-Up

Name the angle relationships.

1. <2 and <6

2. <4 and <6

3. <5 and < 8

4. <1 and <8

5. <3 and <6

Essential Question

What is a reflection? Draw an example of a reflection.

Reflections

Unit 1, Day 4

Common Core GPS

MCC8.G.1: Verify experimentally the properties of rotations, reflections, and translations:

a. Lines are taken to lines, and line segments to line segments of the same length.

b. Angles are taken to angles of the same measure.c. Parallel lines are taken to parallel lines.

MCC8. G. 2: Understand that a two-dimensional figure is congruent to another if the second can be obtained from the first by a sequence of rotations, reflections, and translations; given two congruent figures, describe a sequence that exhibits the congruence between them.

Language of the Standards

Reflection: a transformation that “flips” a figure over a line of reflection.

Reflection Line: a line that is the perpendicular bisector of the segment with endpoints at a pre-image point and the image of that after a reflection.

Reflections

Reflections must take place over a line. We will often see a reflection over the x-axis or the y-axis. For example,

Which line is the figure reflected over?

Name the reflection line.

Name the reflection line.

Compare the Coordinates.

Now, let’s examine the coordinates and their change once reflected.

Compare the Coordinates.

Now, let’s examine the coordinates and their change once reflected.

Let’s Reflect…

Reflect the figure over the x – axis.

Let’s Reflect…

Reflect the figure over the y – axis.

How is the reflection over the y-axis different from the x-axis?

Reflect…

A volunteer to reflect over the x-axis.

Reflect…

A volunteer to reflect over the y-axis.

Congruent or Similar?

Are triangles J and Scongruent or similarand how do you know?

Work Session:

What is the reflection line?

1. 2.

5. What is the line of reflection?

6. Name the vertices (coordinates) of triangle ABC and triangle A’B’C’.

7. Is triangle ABC and triangle A’B’C’ congruent or similar? How do you know?

Differentiation: Using the coordinate plane, create your own polygon and reflect over a reflection line. Remember to use the apostrophes to indicate which figure is the reflected figure. When directed by the teacher, you will trade your polygon with another student. You will list the reflected coordinates for the figure as well as the reflection line.

Closing

Discuss the task and any related questions to check for understanding.