NCERT 5th Class (CBSE) Mathematics: Lines And Angle

ANGLES

Types of Angles

Right, acute, obtuse and straight angles are all types of angles that you have studied so far. There are two more types of angles.

Reflex angle: Look at the railing of this staircase. They from an angle on the outside that is more than 180°.

An angle that is more than 180° and less than 360° is called a reflex angle.

Whole angle: If we draw several angles around a point and measure and add them, we find that they always add up to 360°.

(b) 100 + 45 + 45 + 50 + 120 = 360°

A whole angle measures 360°.

Measuring Reflex Angles

we can use our knowledge of whole angles to measure reflex angles.

Angle Relationships

This electric power line reminds us of many angles and the relationship between them.

Adjacent angles

Angles are adjacent when they have a common arm, the same vertex and do not overlap.

∠AOB is adjacent to ∠BOC as they have the common arm OB and a common vertex O.