Digits, Grade 7, Volume 1, Homework Helper

Topic 4: Circles

4-1: Center, Radius, and Diameter

Key Concept

Parts of a Circle

A circle is the set of all points in a plane that are the same distance from a given point called the center. You name a circle by its center. Circle P is shown.

A diameter is a segment that passes through the center of a circle and has both endpoints on the circle. The term diameter can also mean the length of this segment.

A radius is a segment that has one endpoint at the center and the other endpoint on the circle. The term radius can also mean the length of this segment.

Part 1


You name a segment by its endpoints. Read eh b bar as “segment AB.” The diagram shows eh b bar , comma , b c bar , comma and eh c bar , . .

To refer to the length of a segment, you write the letters without the segment bar. So AB = 3 inches and AC = 3 inches.

Points A, B, and C on a circle. Line segments go from A to B, from B to C, and from C to A. Segments AB and AC are each 3 inches. long.

Example Naming Diameters and Radii of Circles

An art class developed this logo to represent the school in an art show. Determine which segments are radii and which are diameters.

A circle and line segments.

table with 2 rows and 4 columns , row1 column 1 , p c bar , column 2 eh d bar , column 3 eh p bar , column 4 eh b bar , row2 column 1 , eh c bar , column 2 p d bar , column 3 p b bar , end table

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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