# Types of Angles

Types of angles are discussed here according to their degree measure.

Angles are classified on the basis of their measures.

1. Acute Angle:

An angle whose measure is less than 90° is called an acute angle.

In other words, an angle measuring between 0° to 90° is called an acute angle. ∠ABC in the given figure is an acute angle.

∠MON shown in adjoining figure is equal to 60°. So, ∠MON is an acute angle.

2. Right Angle:

An angle whose measure is 90° is called right angle.

In other words, an angle which measure exactly 90° is called a right angle.

Two lines that meet at a right angle are called perpendicular lines.

In the above figure, ∠AOB is a right angle. In this case, we say that the arms OA and OB are perpendicular to each.

Therefore, ∠AOB shown in adjoining figure is 90°.

So, ∠AOB is a right angle.

3. Obtuse Angle:

An angle whose measure is greater than 90° but less than 180° is called an obtuse angle.

In other words, an angle measuring between 90° to 180° is called an obtuse angle.

∠DOQ shown in the above figure is an obtuse angle.

4. Straight Angle:

An angle whose measure is 180° is called a straight angle.

In other words, an angle which measures exactly 180° is called a straight angle.

∠XOY shown in the above figure is a straight angle.

A straight angle is equal to two right angles.

5. Reflex Angle:

An angle whose measure is more than 180° but less than 360° is called a reflex angle.

∠AOB shown in the above figure is 210°.

So, ∠AOB is a reflex angle.

6. Zero Angle:

An angle measure 0° is called a zero angle.

When two arms of an angle lie on each other, angle is formed.

Comparision of Angles

An angle whose degree measure is greater than the degree measure of another angle is a greater angle. Thus, we can say that:

Acute Angle < Right Angle < Obtuse Angle < Straight Angle < Reflex Angle.

Questions and Answers on Types of Angles:

I. Classify the given angles as acute, obtuse, right and straight.

(i) 158°

(ii) 90°

(iii) 36°

(iv) 180°

(v) 91°

(i) Obtuse Angle

(ii) Right Angle

(iii) Acute Angle

(iv) Straight Angle

(v) Obtuse Angle

Interior and Exterior of an Angle.

Measuring an Angle by a Protractor.

Types of Angles.

Pairs of Angles.

Bisecting an angle.

Construction of Angles by using Compass.

Worksheet on Angles.

Geometry Practice Test on angles.