An angle is the space between two lines that meet each other. When two lines meet at a point, an angle is formed. The two lines are called the arms of the angle. The point they meet is called the vertex.
To measure the size of an angle, we use degree. Degree is a standard unit. Degree is denoted by the symbol '°'. A degree can be divided into 60 minutes (1° = 60'), and a minute can be also be divided into 60 seconds (1' = 60"). In mathematics, angles are usually measured in radians.
Types of angles [change]
An acute angle is an angle less than 90°. A right angle is an angle equal to 90°. An obtuse angle is an angle greater than 90° but less than 180°. A straight angle (or straight line) is an angle equal to 180°. A reflex angle is an angle greater than 180° but less than 360°.
Supplementary angles are two angles with the sum equal to 180°.
Two angles that sum to one right angle (90°) are called complementary angles.
Two angles that sum to one full circle (360°) are called explementary angles or conjugate angles.