standard_description: Derive using similarity the fact that the length of the arc intercepted by an angle is proportional to the radius, and define the radian measure of the angle as the constant of proportionality; derive the formula for the area of a sector.
problem_activity: Optional activity
The purpose of this activity is for students to create their own stained-glass design for a given amount of money. The activity is purposefully left open to allow students to either tweak the previous design or create something completely new.
As students work, monitor and select students who either tweaked a previous design or created a new, interesting design to share during the whole-group discussion.
Launch
Students in same groups.  Remind students to include whole or partial circles in their designs.
Student Facing
Draw a stained-glass window design that could be made for less than
$
450. Show your thinking. Organize your work so it can be followed by others.
Student Response
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Anticipated Misconceptions
Some students may think they need to create a new design and struggle getting started. Point these students to the designs in previous activities and ask how they could modify these designs to meet the cost requirement.
Activity Synthesis
Display students’ designs for all to see and ask students to explain how they knew their design met the cost requirement. Allow other students to ask questions of the student who is sharing their design.
Speaking, Listening: MLR7 Compare and Connect.
As students prepare their stained-glass window designs, look for students with different solution methods. As students investigate each other’s work, ask students to share what worked well in a particular approach. During this discussion, listen for and amplify any comments about what might make the calculation of the cost more precise. Then encourage students to make connections between the quantities used to calculate the cost of the glass and the circles in the stained-glass window design. During this discussion, listen for and amplify language students use to interpret quantities as the total area of the whole or partial circles in their design. This will foster students’ meta-awareness and support constructive conversations as they compare strategies for calculating the cost of a stained-glass window and make connections between quantities and the area of circles.
Design Principle(s): Cultivate conversation; Maximize meta-awareness


aligns: no