NCERT Book Class 9 Maths Chapter 3 Coordinate Geometry

CHAPTER 3

COORDINATE GEOMETRY

What’s the good of Mercator’s North Poles and Equators, Tropics, Zones and
Meridian Lines?’ So the Bellman would cry; and crew would reply ‘ They are
merely conventional signs!’
LEWIS CARROLL, The Hunting of the Snark
3.1 Introduction
You have already studied how to locate a point on a number line. You also know how
to describe the position of a point on the line. There are many other situations, in which
to find a point we are required to describe its position with reference to more than one
line. For example, consider the following situations:
I. In Fig. 3.1, there is a main road running
in the East-West direction and streets with
numbering from West to East. Also, on each
street, house numbers are marked. To look for
a friend’s house here, is it enough to know only
one reference point? For instance, if we only
know that she lives on Street 2, will we be able
to find her house easily? Not as easily as when
we know two pieces of information about it,
namely, the number of the street on which it is
situated, and the house number. If we want to
reach the house which is situated in the 2nd
street and has the number 5, first of all we
would identify the 2nd street and then the house
numbered 5 on it. In Fig. 3.1, H shows the
location of the house. Similarly, P shows the
Fig. 3.1
location of the house corresponding to Street
number 7 and House number 4.