Let us see some basics concepts of lines and angles in geometry.

**Straight line**

In geometry, a line is always straight. There is no curve. Its has no limit and it has infinite length.

**Ray**

A ray is a part of a line that has one endpoint and goes on infinitely in only one direction.

**Line Segment**

A line is a part of a straight line. There is no curve. Its has two endpoints and it has a definite length.

**Perpendicular lines**

When two lines meet at a right angle, the lines are said to be perpendicular to each other.

**Complementary angles**

In a right-angled triangle, if sum of two angles is 90° then the two angles are called complementary angles.

∠POQ + ∠QOR= 90°

**Supplementary angles**

In a straight angle, if the sum of two angles is 180° then the two angles are called supplementary angles. Two right-angle always supplementary angles.

∠POR + ∠POQ = ∠POQ = 180°

**Adjacent angles**

Two angles are known as adjacent angles if they have a common vertex and common arm and lies on the same straight line.

∠POR and ∠POQ adjacent angle. ∠POR + ∠POQ = 180°

**Vertically opposite angles**

When two lines intersect, the angles formed opposite to each other at the point of intersection (vertex) are called vertically opposite angles. Two angles that are opposite at vertex are congruent.

∠A & ∠C are vertically opposite angles. Similarly, ∠B & ∠D are vertically opposite angles.

∠A = ∠C & ∠B = ∠D

I hope, this article will help you a lot to understand the **Lines and Angles – Definitions | Properties**. If you still have any doubts and problems with any topic of mathematics you can ask your problem in the Ask Question section. You will get a reply shortly.

**Related Topic:**

Introduction to Angles and Types of Angles

Type Of Angle Made By Parallel Lines Cut By Transversal