CCSS.Math.Content.8.G.A.4
The standard
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.
Common Core State Standards for Mathematics · Geometry
What this standard means
Students need to recognize when two figures have the same shape, even if one has been turned, flipped, slid, or resized. They also need to describe a clear sequence of moves that maps one figure onto the other, including a dilation when the size changes.
Mastery looks like naming the transformations in order and using correct details, such as direction, line of reflection, center of rotation, or scale factor. Students often get stuck by saying figures “look alike” without proof, mixing up congruent and similar, or forgetting that dilation changes size but not shape.
Ways to teach it
- Have students use patty paper to trace a triangle, then slide, flip, turn, and enlarge it on grid paper to match a target triangle.
- Ask students to write: What moves would take Figure A to Figure B, and where does the size change happen?
- Show two grid figures and ask students to list the transformation sequence in three minutes, including any scale factor.
- Use phone photo resizing or map zooming to show how dilation keeps shape while changing size.
Plan a lesson for CCSS.Math.Content.8.G.A.4
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