options: Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles. For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so.

Describe the effect of dilations, translations, rotations, and reflections on two-dimensional figures using coordinates.

Verify experimentally the properties of rotations, reflections, and translations:
- Lines are taken to lines, and line segments to line segments of the same length.
- Angles are taken to angles of the same measure.
- Parallel lines are taken to parallel lines.

Understand that a two-dimensional figure is similar to another if the second can be obtained from the first by a sequence of rotations, reflections, translations, and dilations; given two similar two-dimensional figures, describe a sequence that exhibits the similarity between them.

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.
problem_activity: Task
Below is a picture of a triangle on a coordinate grid:
[IMG]
Draw the reflection of $\triangle ABC$ over the line $x = -2$. Label
the image of $A$ as $A^\prime$, the image of $B$ as  $B^\prime$ and
the image of $C$ as $C^\prime$.
Draw the reflection of $\triangle A^{\prime}B^{\prime}C^\prime$ over the line $x = 2$. Label
the image of $A^\prime $ as $A^{\prime \prime}$, the image of $B^\prime$ as  $B^{\prime \prime}$ and
the image of $C^\prime$ as $C^{\prime \prime}$.
What single rigid transformation of the plane will map $\triangle ABC$ to
$\triangle A^{\prime \prime}B^{\prime \prime}C^{\prime \prime}$?  Explain.


correct_option_index: 1