NCERT Book Class 11 Maths Chapter 9 Straight Lines

Chapter 9
STRAIGHT LINES

vG eometry, as a logical system, is a means and even the most powerful
means to make children feel the strength of the human spirit that is
of their own spirit. – H. FREUDENTHALv

9.1 Introduction
We are familiar with two-dimensional coordinate geometry
from earlier classes. Mainly, it is a combination of algebra
and geometry. A systematic study of geometry by the use
of algebra was first carried out by celebrated French
philosopher and mathematician René Descartes, in his book
‘La Géométry, published in 1637. This book introduced the
notion of the equation of a curve and related analytical
methods into the study of geometry. The resulting
combination of analysis and geometry is referred now as
analytical geometry. In the earlier classes, we initiated
the study of coordinate geometry, where we studied about René Descartes
coordinate axes, coordinate plane, plotting of points in a (1596 -1650)
plane, distance between two points, section formulae, etc. All these concepts are the
basics of coordinate geometry.
Let us have a brief recall of coordinate geometry done in earlier classes. To
recapitulate, the location of the points (6, – 4) and
(3, 0) in the XY-plane is shown in Fig 9.1.
We may note that the point (6, – 4) is at 6 units
distance from the y-axis measured along the positive
x-axis and at 4 units distance from the x-axis
measured along the negative y-axis. Similarly, the
point (3, 0) is at 3 units distance from the y-axis
measured along the positive x-axis and has zero
distance from the x-axis.
We also studied there following important Fig 9.1
formulae: