NY Next Generation Math NY-8.G.1.b

Math8th GradeVerify experimentally the properties of rotations, reflections, and translations.

The Standard

Verify experimentally angles are mapped to angles of the same measure.

New York State Next Generation Mathematics Learning Standards

Teacher's field guide

What Students Need to Do: Students test rotations, reflections, and translations to verify that angle measures stay unchanged. They compare corresponding angles before and after each transformation.
What Mastery Looks Like: The student transforms a figure, measures a 65-degree angle and its image, and records equal measures. The student uses repeated trials to support angle preservation.
Common Misconceptions: Students may think turning or flipping a figure changes its angle measures. They may compare noncorresponding angles or let drawing inaccuracies replace measurement evidence.
How to Assess It: Give a triangle with a 65-degree angle and specify a translation vector, a reflection line, and a rotation center, angle, and direction. Ask students to perform each transformation and measure the corresponding image angle.

Lesson moves

Trace a figure on transparencies, perform each rigid transformation, and measure corresponding angles with a protractor.
Ask students why changing an angle's orientation does not change its measure.
Play angle-image match with original figures, transformed copies, and corresponding-angle measurements.
Test whether angles in a rotated logo or reflected sign design keep their original measures.

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