NCERT Book Class 9 Maths Chapter 2 Polynomials

POLYNOMIALS 25

CHAPTER 2

POLYNOMIALS

2.1 Introduction
You have studied algebraic expressions, their addition, subtraction, multiplication and
division in earlier classes. You also have studied how to factorise some algebraic
expressions. You may recall the algebraic identities :
(x + y)2 = x2 + 2xy + y2
(x – y)2 = x2 – 2xy + y2
and x2 – y2 = (x + y) (x – y)
and their use in factorisation. In this chapter, we shall start our study with a particular
type of algebraic expression, called polynomial, and the terminology related to it. We
shall also study the Remainder Theorem and Factor Theorem and their use in the
factorisation of polynomials. In addition to the above, we shall study some more algebraic
identities and their use in factorisation and in evaluating some given expressions.

2.2 Polynomials in One Variable
Let us begin by recalling that a variable is denoted by a symbol that can take any real
1
value. We use the letters x, y, z, etc. to denote variables. Notice that 2x, 3x, – x, – x
2
are algebraic expressions. All these expressions are of the form (a constant) × x. Now
suppose we want to write an expression which is (a constant) × (a variable) and we do
not know what the constant is. In such cases, we write the constant as a, b, c, etc. So
the expression will be ax, say.
However, there is a difference between a letter denoting a constant and a letter
denoting a variable. The values of the constants remain the same throughout a particular
situation, that is, the values of the constants do not change in a given problem, but the
value of a variable can keep changing.