Page 92 - Revised Maths Wisdom Class - 6

6 Lines and Angles

CHAPTER OUTLINES

● Plane ● Pair of Lines ● Types of Angles
● Point ● Angles ● Drawing Angles by Using Protractor
● Line ● Degree Measure of an Angle ● Angle Bisector
● Line Segment ● Comparison of Angles
● Ray ● Measurement of Angles

RECALL

● A point is a mark of position or location. A point is represented by a dot and capital letters are used to name the points.
● A ray is a part of line. It begins from one point and extends indefinitely only in one direction. It is denoted as AB .
● A line is a straight path that extends indefinitely on both sides. It has no end points and is denoted as AB .
● A line segment is a part of line and has a definite length. It is denoted as AB.
● Two lines in a plane which never meet, however far they are produced are called parallel lines.
● Two distinct lines meeting at a point are called intersecting lines.
● The figure formed by two rays having a common point as an end point is called an angle.
● Different kind of angles are:
(a) zero angle = 0° (b) straight angle = 180°
(c) right angle = 90° (d) complete angle = 360°
(e) Acute angle measures more than 0° but less than 90° (f) Obtuse angle measures more than 90° but less than 180°
(g) Reflex angle measures more than 180° but less than 360°

Introduction
Look around yourself, we observe many geometrical structures like points, lines, rays, angles, triangles,
quadrilaterals and circles. In this chapter we shall learn only basic geometric ideas of these geometrical structures.
Whether it is a dress or a table or huge office building, it is not possible to construct anything unless we have two
things, the shape and the measurement. These two things form the basis of a branch of mathematics known as
geometry.

The geometry began when men felt to need measure their lands while buy and selling. Various shapes and figures
with which we deal in geometry are called geometrical figures.
Today art, architecture engineering and designing make use of various aspects of geometry. Let us therefore learn
some of the basic concepts.