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, **0°** 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°

**Answers:**

(i) Obtuse Angle

(ii) Right Angle

(iii) Acute Angle

(iv) Straight Angle

(v) Obtuse Angle

**● ****Angle.**

**Interior and Exterior of an Angle.**

**Measuring an Angle by a Protractor.**

**Construction of Angles by using Compass.**

**Geometry Practice Test on angles.**

**5th Grade Math Problems**

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