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


Building Towards

Glossary Entries

  • sector

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