SaiBook.us Geometry

Lesson

Title: Angle(Types of angles)

Grade: 4-a Lesson: S2-L1

Explanation: Hello students, let us learn a new topic in geometry today with definitions, concepts, examples, and worksheets included.

Lesson:

Definition: Angle

An angle is formed by the intersection of two lines or rays at a common endpoint, which is called the vertex.

The symbol ∠ represents an angle.

Angles are typically measured in degrees (°) or radians (rad).

$1$

Explanation: The given image shows that OC and OD are the arms of the angle COD.

Definition: Types of Angles

There are six types of angles, including acute angles which measure greater than 0° and less than 90°.

When an angle measures 90°, it is known as a right angle.A right angle can be easily observed as it forms the shape of the letter L.

When an angle measures greater than 90° but less than 180°, it is an obtuse angle.

$2$

Explanation: It shows the acute angle, obtuse angle, and right angle.

Definition: Types of Angles

A straight angle measures 180° and is formed by a straight line. The angle between two rays also measures 180°.

A reflex angle is an angle whose measure is greater than 180° but less than 360°.

When the measurement of an angle is equal to 360°, it is a complete angle.

$3$

Explanation: It shows the straight angle, reflex angle, and complete angle.