What is an Angle?
An angle is formed when two straight lines or rays meet at a common endpoint. The common point of contact is called the vertex of an angle. The word angle comes from a Latin word named ‘angulus,’ meaning “corner.”
Parts of Angles
- Vertex: A vertex is a corner of an angle, a point where two lines/sides meet. O is the vertex in the given figure.
- Arms: The two sides of the angle, joined at a common endpoint. OA and OB are arms of an angle.
- Initial Side: Also known as the reference line, a straight line from where an angle is drawn. OB is the reference line.
- Terminal Side: The side up to which the angle measurement is done. In the given diagram below, OA is the terminal side.
Types of Angles
Here are the different types of angles:
- An acute angle measures less than 90° at the vertex.
- An obtuse angle is between 90° and 180°.
- A right angle precisely measures 90° at the vertex.
- An angle measuring exactly 180° is a straight angle.
- A reflex angle measures between 180°- 360°.
- `A complete angle measure equals 360°.`A complete angle measure equals 360°.
Interior and Exterior Angles:
Interior angles: Interior Angles are the angles formed within or inside a shape.
Here, ∠ABC, ∠BCA and ∠CAB are interior angles.
Exterior angles: Exterior angles are the angles formed outside a shape, between any side of a shape and an extended adjacent side. Here, ∠ACD is an exterior angle.
The sum of all angles around a point equals
360°
180°
270°
90°
Angles that sum up to 90° are known as
vertical angles
complementary angles
reflective angles
supplementary angles
Angles that are opposite to each other when two straight lines intersect each other are called
vertical angles
complementary angles
reflective angles
supplementary angles
When two straight lines intersect each other, the angles that are opposite to each other are called vertical angles.
