Virginia SOL 8.MG.3.b
The Standard
Given a preimage in the coordinate plane, identify the coordinates of the image of a polygon that has been reflected over the x- or y-axis
Virginia Standards of Learning for Mathematics · The student will apply translations and reflections to polygons in the coordinate plane.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students find the new coordinates of polygon vertices after a reflection over the x-axis or y-axis. They apply the correct sign change to each ordered pair.
What Mastery Looks Like
- Students correctly change the sign of the y-coordinate for an x-axis reflection and the x-coordinate for a y-axis reflection. They can plot and label the image accurately.
Common Misconceptions
- Students may swap coordinates instead of changing one sign, or change both signs as if rotating 180 degrees. They may also change coordinates of points that lie on the reflection axis.
How to Assess It
- Exit ticket: Triangle A(2, 1), B(5, 1), and C(3, 4) is reflected over the y-axis. Write the image coordinates.
Lesson moves
Ways to Teach It
Plot a polygon on graph paper, trace it on patty paper, flip the tracing across an axis, and record the new coordinates.
Ask students to explain which coordinate changes during each reflection and why points on the reflection axis stay fixed.
Give pairs cards showing polygons, reflection axes, and coordinate sets, then have them match each preimage with its correct image.
Have students design half of a logo on a coordinate grid, reflect it across the y-axis, and list all image coordinates.
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Related Standards
- 8.MG.3.e
Sketch the image of a polygon that has been reflected over the x- or y-axis.
- 8.MG.3.a
Given a preimage in the coordinate plane, identify the coordinates of the image of a polygon that has been translated vertically, horizontally, or a combination...
- 8.MG.3.f
Sketch the image of a polygon that has been translated and reflected over the x- or y-axis, or reflected over the x- or y-axis and then translated.
- 8.MG.3.c
Given a preimage in the coordinate plane, identify the coordinates of the image of a polygon that has been translated and reflected over the x- or y-axis or ref...
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