standard_description: Explain how the criteria for triangle congruence (ASA, SAS, and SSS) follow from the definition of congruence in terms of rigid motions.
problem_activity: Narrative
This warm-up prompts students to visualize the idea of arranging angles around a point and adding their measurements as more pieces are added. The angles are familiar angles:
\(90^\circ\)
,
\(180^\circ\)
, and
\(270^\circ\)
. Students previously arrived at these benchmarks by decomposing a full turn or
\(360^\circ\)
. Here, they compose a full turn from
\(90^\circ\)
angles.
The work here familiarizes students with the context and mathematics that might be involved later in the lesson. In the subsequent activities, students will compose and decompose paper cutouts of angles to determine angle measurements.
Launch
Groups of 2
Display the image.
“What do you notice? What do you wonder?”
1 minute: quiet think time
Activity
“Discuss your thinking with your partner.”
1 minute: partner discussion
Share and record responses.
Student Facing
What do you notice? What do you wonder?
[IMG]
Student Response
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Activity Synthesis
“What angles do you think are the measurement of each angle?” (They look like
\(90^\circ\)
,
\(180^\circ\)
, and
\(270^\circ\)
angles.)
“How do you know?” (If the paper is a rectangle, then the corner pieces are right angles or
\(90^\circ\)
each. Two of the corner pieces would be
\(90+90\)
. Three pieces would be
\(90+ 90+90\)
.)
“What angle would we get if we add the last corner piece?” (
\(360^\circ\)
)


aligns: no