Page 153 - Maths Skills - 7

Lines and Angles 151

INTRODUCTION
You have already known how to identify different lines, line segments and angles in a given shape.
Let us revise them.

LINE SEGMENT

Line segment is the shortest distance between any two points. It has two end points. It cannot be extended in any
direction. A line segment can be measured, so, it has finite length.

AB is a line segment. It is denoted as AB .

LINE
A line segment extended in both the directions becomes a line.
A line has no end point. It can be extended endlessly in both the directions. We can say that a line has infinite
length that cannot be measured.
Line segment is a part of line.

XY is a line, it is denoted as .
XY
RAY
A line segment when extended in one direction only, becomes a ray. It has one initial point. It has no finite length.

Here OX is a ray. It is denoted as OX . It has O as its initial point.

ANGLE
Two rays having same initial point form an angle. An angle can also be formed when lines or line segments meet
or intersect each other at a point.

TYPES OF ANGLES

Acute angle
An angle whose measure is less than right angle is called an acute angle. ∠ABC is an
acute angle.

Obtuse angle
An angle whose measure is greater than 90° but less than 180° is called an obtuse
angle. ∠DEF is an obtuse angle.

Right angle
An angle whose measure is equal to 90° is called a right-angle. ∠ABC is a right angle
as its measure is 90°.

Straight angle
An angle whose arms form opposite rays is a straight angle. Its measure is 180°.
Here ∠AOB is a straight angle. 180º