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8th Grade Math Lesson
Excerpt From this Document
BAND: Transformations- 8.G. 9
Aim: Students will be able to identify and describe reflections over a given line
Language Objective: Reflection, Line of symmetry, Image.
- Mini-lesson: Review definition of Reflection Line of Symmetry Go over rules of reflection over X-Axis, Y-Axis and Line y=x.
- Examples: Reflect over the X-Axis, Y-Axis and over the line Y=X the following triangle. A (1, 3) B (2, 5) C (5, 1)
- H-A-G: Reflect a triangle whose coordinates are M(1, -3), N(2, -4), O( 4, -8). Reflect it over the x-axis, and the y-axis.
- Work period: Students work in their expert groups. They use their grade 8 mathematics pages 231-233 for activity A. Students use their NYS 8TH Math pages 162-164 for activity B
- On a coordinate plane, the following rule applies to the coordinates of a point and its image after a reflection in the y-axis.
- P(x , y)→P’(-x , y) For example: the point (2 , 3) will become (-2 , 3) under a reflection in the y-axis.
Try this: Give the coordinates of the point after a reflection in the y-axis.
- D (4, 3)→ D’ ( , )
- E (5, -1)→ E’ ( , )
- F (-8, -6)→ F’ ( , )
Summary of Ideas
- The order in which the original figure was labeled was reversed in the image after the reflection.
- The shape of the original figure did not change in the image after thereflection.
- The size of the original figure did not change in the image after the reflection.
- Each point and its image are equidistant from the line of reflection.
- In a reflection, only the x-coordinate becomes negative after a reflection in the y-axis.
About this Document
STRAND: Geometry BAND: Transformations- 8.G. 9 Aim: Students will be able to identify and describe reflections over a given line