Types of angles : Depending on their measure, angles can be classified as acute angle, right angle or obtuse angle.

Right angle : The right angle ( figure 1.17 ) has a measure of 90⁰. It is represented by the symbol . Since its measure is fixed, it follows that all right angles are equal. Ð AOB (figure 1.17 ) is a right angle.

Figure 1.17

Acute angle : Any angle whose measure is between 0 and 90⁰ is called an acute angle (figure 1.18).

Figure 1.18

0 < a < 90 \ a is an acute angle.

Obtuse angle : An angle with a measure between 0⁰ and 180⁰ is called an obtuse angle (figure 1.19).

Figure 1.19

90⁰ < b < 180⁰ \ b is an obtuse angle.

Index

Introduction

1.1 Points, Lines and Planes
1.2 Line Segment
1.3 Rays and Angles
1.4 Some Special Angles
1.5 Angles made by a Transversal
1.6 Transversal Across Two Parallel Lines
1.7 Conditions for Parallelism

Chapter 2