Area of Sectors in Circles

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SWBAT derive formula for area of sector in a circle and apply formula.

Big Idea

After watching a BrainPop! students will derive the formula for area of a sector and apply these to problems.

Do Now, Brain Pop!

25 minutes

Students will complete two Do Now questions that review how to find the central angle of circle and also how to find the length of a chord using Pythagorean Theorem.  Teachers may want to also review key terms like semicircle for the upcoming lesson.


After reviewing the agenda and objective for this lesson, teachers can show a BrainPop! that highlights the key formulas related to circles, like circumference and area.  Following the BrainPop!, students can complete three pair-share questions asking them to find the area and circumference of disks as well as determining the use of disks in ancient Greece.  From this pair-share, students can jump into the “exploration” portion of the lesson, which we will discuss in middle section of lesson in a video narrative.  

Pair-Share, Exploration and Notes

35 minutes

Activity/Homework and Exit Ticket

20 minutes

To complete the last part of this lesson, students can use their compass and ruler to complete the “Activity” which asks students to draw a diagram and then find the area and circumference of one-eighth of a circle.  This could be an independent activity or one which students work in small groups to complete.  I find that students enjoy completing this hands-on task, and incorporates a lot of great skills, like drawing a circle with given measurements and also dividing circles into congruent parts. 

Teachers can de-brief this activity or collect a copy from students to check their understanding.  If time remains, students can complete the practice questions, but I would emphasis reviewing the activity before reviewing the practice examples if time class time remains.   At the end of class, teachers can ask students to complete the exit ticket which asks students to find the area of a sector of a circle.