Lines and Angles – Definitions | Properties

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.

Line - mathsmaker.com

Ray

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

Ray - mathsmaker.com

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.

Line Segment - mathsmaker.com

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°
 Complementary angles - mathsmaker.com

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°

Supplementary angle, maths - mathsmaker.com

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

Vertically opposite angles - mathsmaker.com

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Related Topic:

Introduction to Angles and Types of Angles
Type Of Angle Made By Parallel Lines Cut By Transversal

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