*Some ideas for sentence frames/starters that could be incorporated into your lesson are listed below. If you think a sentence frame/starter will be helpful, consider how will it support students’ mathematical learning and/or development of academic language, and decide which sentence frame/starter (from the list below or that you create) would best support students’ learning. You may find that the starters and frames vary in level of difficulty, and plan to provide them to students accordingly.*

## Starters

When I fold the top left corner of a non-square rectangle to meet the bottom right corner, the triangles that are reflected over the fold are: __________________________________________________________________________________________________

For all sizes of non-square rectangles, if I fold the top left corner to meet the bottom right corner: __________________________________________________________________________________________________________________________________

Triangles EDC and FGC are alike in that they both_________________________________________________________________

## Frames

When I fold the top left corner of a non-square _______________ to meet the bottom right corner, the _________________ that are congruent.

fold are: __________________________________________________________________________________________________

Triangle EDC and Triangle FGC are ____________________ because _________________________________________________

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### Academic Language

*Students should have opportunities to see, hear, and write key mathematical ideas during this activity. There are some specific terms that students need to understand in order to engage in this task, and there are some additional terms and phrases that may surface as the students engage with the task. You may think of additional words or phrases that are key to this activity. As the task is introduced, solved by the students, and discussed, ensure that students have opportunities to experience (i.e., through discussion, pictures, and the use of gestures) and to build understanding for key words and phrases. Examples of words and phrases that may be involved in work on this problem include:*

- congruence; congruent
- reflection/reflect; translation/translate; rotation/rotate; reflected onto
- turn; slide; flip
- square; triangle
- non-square rectangle
- isosceles; isosceles triangles; isosceles right triangles
- diagonal
- line of reflection; line of symmetry
- similar; alike
- perpendicular bisector
- right angle
- line segment
- angle
- fold