Lesson 8
Arcs and Sectors
Lesson Narrative
In this lesson, students investigate circle sectors. A sector is a region of a circle enclosed between 2 radii. Students look for and express regularity in repeated reasoning (MP8) as they make sector area and arc length calculations and use their findings to create a general method for finding sector areas and arc lengths.
Building intuition about arc length and fractions of circles will be helpful as students develop a definition of radian measure in an upcoming lesson.
Learning Goals
Teacher Facing
 Generalize (orally and in writing) methods for calculating lengths of arcs and areas of sectors in circles.
Student Facing
 Let’s analyze portions of circles.
Learning Targets
Student Facing
 I can calculate lengths of arcs and areas of sectors in circles.
CCSS Standards
Building On
Addressing
Building Towards
Glossary Entries

sector
The region inside a circle lying between two radii of the circle.
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