standard_description: Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles. For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so.
problem_activity: Narrative
The purpose of this warm-up is for students to participate in part of the Questions About Us routine. Students have worked with 5-frames in previous sections and as an option during counting collections. In this activity, 5-frames are introduced as a way to represent how many students are here today. A blackline master is provided, but the 5-frames should be modified to match the number of students in the class. For example, if there are 24 students in the class, four 5-frames and 4 extra squares should be displayed. This will allow students to use the representation to also determine how many students are absent in future lessons by referring to the empty squares. This display will be used during the  Questions About Us warm-up in later lessons, so create the display in a place in the classroom that can easily be seen by students.
In the synthesis, students look at the new 5-frame representation and compare it to the representations based on student ideas created in the previous lesson.
Required Materials
Materials to Gather
Chart paper
Materials to Copy
Questions About Us 5-Frames
Required Preparation
Gather the poster created during Questions about Us in the previous lesson.
Launch
“How can we use the 5-frames to show how many of us are here?”
30 seconds: quiet think time
1 minute: partner discussion
Share responses.
Activity
Demonstrate a student suggestion for how to use the 5-frames.
“How can we figure out how many of us are here?” (We can count each person. We can count each circle in the 5-frame.)
Count each student.
“How many of us are here today?”
Count each circle.
“How many of us are here today?”
Student Response
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Activity Synthesis
Display one of the representations based on student ideas from the previous lesson and the new representation with 5-frames.
“These are both different ways that we showed how many of us are here. What do you notice?”


aligns: no