Angle and it's classification
An angle is the figure formed by two rays with a common endpoint. The two rays are called the sides and the common initial point is the vertex. If the angle is considered as a turning ray, the starting position is called the initial side and the other is called terminal side. Angle are measured by a unit called degree and the instrument used is the protractor.
Vertical angles are two angles in which the sides of one angle are opposite rays to the sides of the other angle.
Classification
A zero angle is one whose measure is 0º. The initial side may be considered as not having moved.
An acute angle is an angle whose measure is greater than 0º but less than 90º.
A right angle is an angle whose measure is exactly 90º.
An obtuse angle is an angle whose measure is greater than 90º but less than 180º.
A straight angle is an angle which measures exactly 180º.
A reflex angle is an angle whose measure is greater than 180º but less than 360º.
Angle pairs
Adjacent angles if two angles have a common vertex and a common side between them.
Linear pair if two adjacent angles, have their non-common sides forming a straight line or opposite rays.
Supplementary if the sum of two angles equals 180º.
Complementary if the sum of two angles equals 90º