Basic Terms and Definitions

We know that a part (or portion) of a line with two end points is called a line-segment while and a part of a line with one end point is called a raysegment.

We are also aware that the symbols used for denoted them are:

Element	Symbol
Line AB
Line Segment PQ	PQ
Ray XY

If three or more points lie on the same line, they are called points.

Otherwise they are known as non-collinear points.

We know that when an angle is formed two originate from the same end point.

The rays making an angle are called the of the angle and the common end point is called the of the angle.

An angle has a measure ranging from 0° and 90° while a angle is exactly equal to 90°.

An angle greater than 90° but less than 180° is called an angle.

A straight angle is equal to °. An angle which is greater than 180° but less than 360° is called a angle.

Further, when two angles measures have a sum equal to 90°, they are known as angles and when the sum of measures is equal to 180°, the two angles are called angles.

Two angles are , if they have a common vertex, a common arm and their non-common arms are on either sides of the common arm.

Adjacent Angles

When two angles are adjacent: their sum is always equal to the angle formed by the two non-common arms.

If the non-common arms form a straight line then the angles are called linear none of the options perpendicular pair of angles.

Linear pair of Angles

When two lines, intersect each other at a point, two vertically opposite angles are formed, which are always .

Vertically opposite angles