Geometry

Lesson 9

Math

Unit 6

7th Grade

Lesson 9 of 21

Objective


Solve real-world and mathematical problems using the relationship between the area of a circle and its radius.

Common Core Standards


Core Standards

  • 7.G.B.4 — Know the formulas for the area and circumference of a circle and use them to solve problems; give an informal derivation of the relationship between the circumference and area of a circle.

Criteria for Success


  1. Know the formula that relates the area and radius of a circle: $${{A=\pi r^2}}$$.
  2. Use the formula $${{A=\pi r^2}}$$ to solve problems.

Tips for Teachers


Lessons 8 and 9 focus on the relationship between a circle’s area and its radius. In Lesson 9, students will solve real-world and mathematical problems involving area. Students will solve more problems involving all measurements of circles in Lessons 10 and 11.

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Anchor Problems


Problem 1

Suzanne is making a circular table of out a square piece of wood. The diameter of the circle she is cutting is 6 feet. How much waste will she have for this project? Express your answer to the nearest square foot.

Guiding Questions

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References

EngageNY Mathematics Grade 7 Mathematics > Module 3 > Topic C > Lesson 17Example 3

Grade 7 Mathematics > Module 3 > Topic C > Lesson 17 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Modified by Fishtank Learning, Inc.

Problem 2

Recall the image below from Lesson 7, composed of a square and two semi-circles. Find the area of the figure. 

Guiding Questions

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Problem 3

A 12 ft. rope is attached to the wall of a garage. A dog’s collar is attached to the end of the rope to allow him to safely stay outside. What is the area of the space the dog has outside?

Guiding Questions

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Problem Set

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Target Task


A circular platter fits exactly into a box. The base of the box is a square with side lengths 24 cm. 

What is the area of the circular platter? 

Student Response

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Additional Practice


The following resources include problems and activities aligned to the objective of the lesson that can be used for additional practice or to create your own problem set.

  • Include problems with composite shapes including simple quadrilaterals, triangle, and circles or semi-circles.
  • Include problems where students determine the percent increase in area from one circle to another; for example, a medium pizza has a diameter of 14 inches and a large pizza has a diameter of 16 inches. By what percent is the area of the large pizza greater than the medium pizza?
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Lesson 8

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Lesson 10

Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Angle Relationships

Topic B: Circles

Topic C: Building Polygons and Triangles

Topic D: Solid Figures

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