standard_description: Derive the formula A = 1/2 ab sin(C) for the area of a triangle by drawing an auxiliary line from a vertex perpendicular to the opposite side.
problem_activity: Narrative
This warm-up prompts students to examine a diagram representing equal groups of non-unit fractions. The understandings elicited here allow students to discuss the relationship between the product of a whole number and a unit fraction and that of a whole number and a non-unit fraction with the same denominator.
Launch
Groups of 2
Display the image.
Activity
“What do you notice? What do you wonder?”
1 minute: quiet think time
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
If no students notice or wonder about equal groups, ask, “What groups do you see and how do you see them?” (4 wholes, each whole has
\(\frac{2}{3}\)
shaded)
“How many thirds do you see?” (8 thirds)
“How are these diagrams different than those we've seen so far in this unit?” (Previously, each whole has only one shaded part. These have two shaded parts each.)
“Today, we will think about situations that involve equal groups but now each group has non-unit fractions.”


aligns: no