Digits, Grade 7, Volume 1, Homework Helper

4-3: Area of a Circle

Key Concept

The formula for area of a circle is A = π r2.

A circle of radius r divided into 8 equal sectors with half of the circumference labeled ½ C. The sectors are arranged side by side to form a parallelogram of approximate base b and height h = r.

Part 1

Example Finding Areas of Circles

The distance of intense shaking from the epicenter of a particular earthquake to the outer edge was about 134 miles. To the nearest square mile, what was the area of intense shaking?

Use 3.14 for π.

Solution

The distance from the epicenter of the earthquake to the outer edge is about 134 miles. This is the radius of a circle.

table with 4 rows and 2 columns , row1 column 1 , eh , column 2 equals pi , r squared , row2 column 1 , , column 2 almost equal to , 3.14 , middle dot , 134 squared , row3 column 1 , , column 2 equals , 3.14 , middle dot 17 comma 956 , row4 column 1 , , column 2 equals 56 comma , 381.84 , end table

The area of intense shaking was about 56,382 mi2.


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Table of Contents

Digits, Grade 7, Volume 1, Homework Helper Unit A: Number and Operations Unit B: Expressions, Equations, and Relationships Unit C: Measurement and Geometry Unit D: Proportionality English/Spanish Glossary Formulas Math Symbols Formulas Measures Properties