# 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.

### Student Facing

• I can calculate lengths of arcs and areas of sectors in circles.

Building On

Addressing

Building Towards

### Glossary Entries

• sector

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

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