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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