Unit C: Measurement and Geometry

Topic 3: Angles

3-1: Measuring Angles

Part 1

Intro

An angle (∠) is a figure formed by two rays with a common endpoint. You can name the angle shown ∠ ABC, ∠ CBA, ∠ B, or ∠ 1. The vertex of an angle is the point of intersection of the two sides of an angle.

Two rays form an angle. The shared endpoint of the two rays is labeled B. A is a point on one ray and C is a point on the other ray. The angle between the rays is labeled 1.

You measure angles in units called degrees (°). You can use a protractor to measure angles.

Step 1 Place the point of the protractor on the vertex of the angle.

Step 2 Make sure that the lower side of the angle passes through zero on the scale. Start measuring from zero.

Step 3 Read the scale where it intersects the higher side of the angle.

A protractor measuring angle ABC. Ray BC passes through the zero-mark. Ray AB passes through the 45-mark. Angle ABC measures 45°.

Sometimes you have to rotate the protractor to line it up with one side of an angle. The lower side of the angle should go through the zero on the protractor's scale.

A protractor measuring angle ABC. Ray BC passes through the zero-mark. Side AB passes through the 60-mark. Angle ABC measures 60°.


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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