Types of angles are discussed here according to their degree measure.
1. Acute Angle:
An angle whose measure is less than 90° is called 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 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.
∠DOQ shown in the above figure is an obtuse angle.
4. Straight Angle:
An angle whose measure is 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.