NCERT Textbook - Algebraic Expressions Class 7 Notes | EduRev

 Page 1


ALGEBRAIC EXPRESSIONS 229 229 229 229 229
12.1  INTRODUCTION
We have already come across simple algebraic expressions like x + 3,  y – 5, 4x + 5,
10y – 5 and so on. In Class VI, we have seen how these expressions are useful in formulating
puzzles and problems. W e have also seen examples of several expressions in the chapter on
simple equations.
Expressions are a central concept in algebra. This Chapter is devoted to algebraic
expressions. When you have studied this Chapter, you will know how algebraic
expressions are formed, how they can be combined, how we can find their values and
how they can be used.
12.2  HOW ARE EXPRESSIONS FORMED?
We now know very well what a variable is. We use letters x, y, l, m, ... etc. to denote
variables. A variable can take various values. Its value is not fixed. On the other hand, a
constant has a fixed value. Examples of constants are: 4, 100, –17, etc.
W e combine variables and constants to make algebraic expressions. For this, we use the
operations of addition, subtraction, multiplication and division. W e have already come across
expressions like 4x + 5, 10y – 20. The expression 4x + 5 is obtained from the variable x, first
by multiplying x by the constant 4 and then adding the constant 5 to the product. Similarly,
10y – 20 is obtained by first multiplying y by 10 and then subtracting 20 from the product.
The above expressions were obtained by combining variables with constants. We can
also obtain expressions by combining variables with themselves or with other variables.
Look at how the following expressions are obtained:
x
2
, 2y
2
, 3x
2
 – 5, xy, 4xy + 7
(i) The expression x
2
 is obtained by multiplying the variable x by itself;
x × x = x
2
Just as 4 × 4 is written as 4
2
, we write x × x = x
2
. It is commonly read as x squared.
Chapter  12
Algebraic
Expressions
Page 2


ALGEBRAIC EXPRESSIONS 229 229 229 229 229
12.1  INTRODUCTION
We have already come across simple algebraic expressions like x + 3,  y – 5, 4x + 5,
10y – 5 and so on. In Class VI, we have seen how these expressions are useful in formulating
puzzles and problems. W e have also seen examples of several expressions in the chapter on
simple equations.
Expressions are a central concept in algebra. This Chapter is devoted to algebraic
expressions. When you have studied this Chapter, you will know how algebraic
expressions are formed, how they can be combined, how we can find their values and
how they can be used.
12.2  HOW ARE EXPRESSIONS FORMED?
We now know very well what a variable is. We use letters x, y, l, m, ... etc. to denote
variables. A variable can take various values. Its value is not fixed. On the other hand, a
constant has a fixed value. Examples of constants are: 4, 100, –17, etc.
W e combine variables and constants to make algebraic expressions. For this, we use the
operations of addition, subtraction, multiplication and division. W e have already come across
expressions like 4x + 5, 10y – 20. The expression 4x + 5 is obtained from the variable x, first
by multiplying x by the constant 4 and then adding the constant 5 to the product. Similarly,
10y – 20 is obtained by first multiplying y by 10 and then subtracting 20 from the product.
The above expressions were obtained by combining variables with constants. We can
also obtain expressions by combining variables with themselves or with other variables.
Look at how the following expressions are obtained:
x
2
, 2y
2
, 3x
2
 – 5, xy, 4xy + 7
(i) The expression x
2
 is obtained by multiplying the variable x by itself;
x × x = x
2
Just as 4 × 4 is written as 4
2
, we write x × x = x
2
. It is commonly read as x squared.
Chapter  12
Algebraic
Expressions
MATHEMATICS 230 230 230 230 230
(Later, when you study the chapter ‘Exponents and Powers’ you will realise that x
2
may also be read as x raised to the power 2).
In the same manner, we can write x × x × x = x
3
Commonly, x
3
 is read as ‘x cubed’. Later, you will realise that x
3
 may also be read
as x raised to the power 3.
x, x
2
, x
3
, ... are all algebraic expressions obtained from x.
(ii) The expression 2y
2
 is obtained from y:2y
2
 = 2 × y × y
Here by multiplying y with y we obtain y
2
 and then we multiply y
2
 by the constant 2.
(iii) In (3x
2
 – 5) we first obtain x
2
, and multiply it by 3 to get 3x
2
.
From 3x
2
, we subtract 5 to finally arrive at 3x
2
 – 5.
(iv) In xy, we multiply the variable x with another variable y. Thus,
x × y = xy.
 (v) In 4xy + 7, we first obtain xy, multiply it by 4 to get 4xy and add
7 to 4xy to get the expression.
12.3  TERMS OF AN EXPRESSION
W e shall now put in a systematic form what we have learnt above about how expressions
are formed. For this purpose, we need to understand what terms of an expression and
their factors are.
Consider the expression (4x + 5). In forming this expression, we first formed 4x
separately as a product of 4 and x and then added 5 to it. Similarly consider the expression
(3x
2
 + 7y). Here we first formed 3x
2
 separately as a product of 3, x and x. We then
formed 7y separately as a product of 7 and y. Having formed 3x
2
 and 7y separately, we
added them to get the expression.
Y ou will find that the expressions we deal with can always be seen this way. They
have parts which are formed separately and then added. Such parts of an expression
which are formed separately first and then added are known as terms. Look at the
expression (4x
2
 – 3xy). We say that it has two terms, 4x
2
 and –3xy. The term 4x
2
 is a
product of 4, x and x, and the term (–3xy) is a product of (–3), x and y.
Terms are added to form expressions. Just as the terms 4x and 5 are added to
form the expression (4x + 5), the terms 4x
2
 and (–3xy) are added to give the expression
(4x
2
 – 3xy). This is because 4x
2
 + (–3xy) = 4x
2
 – 3xy.
Note, the minus sign (–)  is included in the term. In the expression 4x
2
 –3xy, we
took the term as (–3xy) and not as (3xy). That is why we do not need to say that
terms are ‘added or subtracted’ to form an expression; just ‘added’ is enough.
Factors of a term
We saw above that the expression (4x
2
 – 3xy) consists of two terms 4x
2
 and –3xy. The
term 4x
2
 is a product of 4, x and x; we say that 4, x and x are the factors of the term 4x
2
.
A term is a product of its factors. The term –3xy is a product of the factors –3, x and y.
Describe how the
following expressions
are obtained:
7xy + 5, x
2
y, 4x
2
 – 5x
TRY THESE
Page 3


ALGEBRAIC EXPRESSIONS 229 229 229 229 229
12.1  INTRODUCTION
We have already come across simple algebraic expressions like x + 3,  y – 5, 4x + 5,
10y – 5 and so on. In Class VI, we have seen how these expressions are useful in formulating
puzzles and problems. W e have also seen examples of several expressions in the chapter on
simple equations.
Expressions are a central concept in algebra. This Chapter is devoted to algebraic
expressions. When you have studied this Chapter, you will know how algebraic
expressions are formed, how they can be combined, how we can find their values and
how they can be used.
12.2  HOW ARE EXPRESSIONS FORMED?
We now know very well what a variable is. We use letters x, y, l, m, ... etc. to denote
variables. A variable can take various values. Its value is not fixed. On the other hand, a
constant has a fixed value. Examples of constants are: 4, 100, –17, etc.
W e combine variables and constants to make algebraic expressions. For this, we use the
operations of addition, subtraction, multiplication and division. W e have already come across
expressions like 4x + 5, 10y – 20. The expression 4x + 5 is obtained from the variable x, first
by multiplying x by the constant 4 and then adding the constant 5 to the product. Similarly,
10y – 20 is obtained by first multiplying y by 10 and then subtracting 20 from the product.
The above expressions were obtained by combining variables with constants. We can
also obtain expressions by combining variables with themselves or with other variables.
Look at how the following expressions are obtained:
x
2
, 2y
2
, 3x
2
 – 5, xy, 4xy + 7
(i) The expression x
2
 is obtained by multiplying the variable x by itself;
x × x = x
2
Just as 4 × 4 is written as 4
2
, we write x × x = x
2
. It is commonly read as x squared.
Chapter  12
Algebraic
Expressions
MATHEMATICS 230 230 230 230 230
(Later, when you study the chapter ‘Exponents and Powers’ you will realise that x
2
may also be read as x raised to the power 2).
In the same manner, we can write x × x × x = x
3
Commonly, x
3
 is read as ‘x cubed’. Later, you will realise that x
3
 may also be read
as x raised to the power 3.
x, x
2
, x
3
, ... are all algebraic expressions obtained from x.
(ii) The expression 2y
2
 is obtained from y:2y
2
 = 2 × y × y
Here by multiplying y with y we obtain y
2
 and then we multiply y
2
 by the constant 2.
(iii) In (3x
2
 – 5) we first obtain x
2
, and multiply it by 3 to get 3x
2
.
From 3x
2
, we subtract 5 to finally arrive at 3x
2
 – 5.
(iv) In xy, we multiply the variable x with another variable y. Thus,
x × y = xy.
 (v) In 4xy + 7, we first obtain xy, multiply it by 4 to get 4xy and add
7 to 4xy to get the expression.
12.3  TERMS OF AN EXPRESSION
W e shall now put in a systematic form what we have learnt above about how expressions
are formed. For this purpose, we need to understand what terms of an expression and
their factors are.
Consider the expression (4x + 5). In forming this expression, we first formed 4x
separately as a product of 4 and x and then added 5 to it. Similarly consider the expression
(3x
2
 + 7y). Here we first formed 3x
2
 separately as a product of 3, x and x. We then
formed 7y separately as a product of 7 and y. Having formed 3x
2
 and 7y separately, we
added them to get the expression.
Y ou will find that the expressions we deal with can always be seen this way. They
have parts which are formed separately and then added. Such parts of an expression
which are formed separately first and then added are known as terms. Look at the
expression (4x
2
 – 3xy). We say that it has two terms, 4x
2
 and –3xy. The term 4x
2
 is a
product of 4, x and x, and the term (–3xy) is a product of (–3), x and y.
Terms are added to form expressions. Just as the terms 4x and 5 are added to
form the expression (4x + 5), the terms 4x
2
 and (–3xy) are added to give the expression
(4x
2
 – 3xy). This is because 4x
2
 + (–3xy) = 4x
2
 – 3xy.
Note, the minus sign (–)  is included in the term. In the expression 4x
2
 –3xy, we
took the term as (–3xy) and not as (3xy). That is why we do not need to say that
terms are ‘added or subtracted’ to form an expression; just ‘added’ is enough.
Factors of a term
We saw above that the expression (4x
2
 – 3xy) consists of two terms 4x
2
 and –3xy. The
term 4x
2
 is a product of 4, x and x; we say that 4, x and x are the factors of the term 4x
2
.
A term is a product of its factors. The term –3xy is a product of the factors –3, x and y.
Describe how the
following expressions
are obtained:
7xy + 5, x
2
y, 4x
2
 – 5x
TRY THESE
ALGEBRAIC EXPRESSIONS 231 231 231 231 231
We can represent the terms and factors of
the terms of an expression conveniently and
elegantly by a tree diagram. The tree for the
expression (4x
2
 – 3xy) is as shown in the
adjacent figure.
Note, in the tree diagram, we have used
dotted lines for factors and continuous lines for
terms. This is to avoid mixing them.
Let us draw a tree diagram for the expression
5xy + 10.
The factors are such that they cannot be
further factorised. Thus we do not write 5xy as
5 × xy, because xy can be further factorised.
Similarly , if x
3
 were a term, it would be written as
x × x × x and not x
2
 × x. Also, remember that
1 is not taken as a separate factor.
Coefficients
W e have learnt how to write a term as a product of factors.
One of these factors may be numerical and the others algebraic
(i.e., they contain variables). The numerical factor is said to be
the numerical coefficient or simply the coefficient of the term.
It is also said to be the coefficient of the rest of the term (which
is obviously the product of algebraic factors of the term). Thus
in 5xy, 5 is the coefficient of the term. It is also the coefficient
of xy. In the term 10xyz, 10 is the coefficient of xyz, in the
term –7x
2
y
2
, –7 is the coefficient of x
2
y
2
.
When the coefficient of a term is +1, it is usually omitted.
For example, 1x is written as x; 1 x
2
y
2
 is written as x
2
y
2
 and
so on. Also, the coefficient (–1) is indicated only by the
minus sign. Thus (–1) x is written as – x; (–1) x
2 
y
2
 is
written as – x
2 
y
2
 and so on.
Sometimes, the word ‘coefficient’ is used in a more general way . Thus
we say that in the term 5xy, 5 is the coefficient of xy, x is the coefficient of 5y
and y is the coefficient of 5x. In 10xy
2
, 10 is the coefficient of xy
2
, x is the
coefficient of 10y
2
 and y
2
 is the coefficient of 10x. Thus, in this more general
way , a coefficient may be either a numerical factor or an algebraic factor or
a product of two or more factors. It is said to be the coefficient of the
product of the remaining factors.
EXAMPLE 1 Identify , in the following expressions, terms which are not
constants. Give their numerical coefficients:
xy + 4, 13 – y
2
, 13 – y + 5y
2
, 4p
2
q – 3pq
2
 + 5
TRY THESE
1. What are the terms in the
following expressions?
Show how the terms are
formed. Draw a tree diagram
for each expression:
8y + 3x
2
, 7mn – 4, 2x
2
y.
2. Write three expression each
having 4 terms.
Identify the coefficients
of the terms of following
expressions:
4x – 3y, a + b + 5, 2y + 5, 2xy
TRY THESE
Page 4


ALGEBRAIC EXPRESSIONS 229 229 229 229 229
12.1  INTRODUCTION
We have already come across simple algebraic expressions like x + 3,  y – 5, 4x + 5,
10y – 5 and so on. In Class VI, we have seen how these expressions are useful in formulating
puzzles and problems. W e have also seen examples of several expressions in the chapter on
simple equations.
Expressions are a central concept in algebra. This Chapter is devoted to algebraic
expressions. When you have studied this Chapter, you will know how algebraic
expressions are formed, how they can be combined, how we can find their values and
how they can be used.
12.2  HOW ARE EXPRESSIONS FORMED?
We now know very well what a variable is. We use letters x, y, l, m, ... etc. to denote
variables. A variable can take various values. Its value is not fixed. On the other hand, a
constant has a fixed value. Examples of constants are: 4, 100, –17, etc.
W e combine variables and constants to make algebraic expressions. For this, we use the
operations of addition, subtraction, multiplication and division. W e have already come across
expressions like 4x + 5, 10y – 20. The expression 4x + 5 is obtained from the variable x, first
by multiplying x by the constant 4 and then adding the constant 5 to the product. Similarly,
10y – 20 is obtained by first multiplying y by 10 and then subtracting 20 from the product.
The above expressions were obtained by combining variables with constants. We can
also obtain expressions by combining variables with themselves or with other variables.
Look at how the following expressions are obtained:
x
2
, 2y
2
, 3x
2
 – 5, xy, 4xy + 7
(i) The expression x
2
 is obtained by multiplying the variable x by itself;
x × x = x
2
Just as 4 × 4 is written as 4
2
, we write x × x = x
2
. It is commonly read as x squared.
Chapter  12
Algebraic
Expressions
MATHEMATICS 230 230 230 230 230
(Later, when you study the chapter ‘Exponents and Powers’ you will realise that x
2
may also be read as x raised to the power 2).
In the same manner, we can write x × x × x = x
3
Commonly, x
3
 is read as ‘x cubed’. Later, you will realise that x
3
 may also be read
as x raised to the power 3.
x, x
2
, x
3
, ... are all algebraic expressions obtained from x.
(ii) The expression 2y
2
 is obtained from y:2y
2
 = 2 × y × y
Here by multiplying y with y we obtain y
2
 and then we multiply y
2
 by the constant 2.
(iii) In (3x
2
 – 5) we first obtain x
2
, and multiply it by 3 to get 3x
2
.
From 3x
2
, we subtract 5 to finally arrive at 3x
2
 – 5.
(iv) In xy, we multiply the variable x with another variable y. Thus,
x × y = xy.
 (v) In 4xy + 7, we first obtain xy, multiply it by 4 to get 4xy and add
7 to 4xy to get the expression.
12.3  TERMS OF AN EXPRESSION
W e shall now put in a systematic form what we have learnt above about how expressions
are formed. For this purpose, we need to understand what terms of an expression and
their factors are.
Consider the expression (4x + 5). In forming this expression, we first formed 4x
separately as a product of 4 and x and then added 5 to it. Similarly consider the expression
(3x
2
 + 7y). Here we first formed 3x
2
 separately as a product of 3, x and x. We then
formed 7y separately as a product of 7 and y. Having formed 3x
2
 and 7y separately, we
added them to get the expression.
Y ou will find that the expressions we deal with can always be seen this way. They
have parts which are formed separately and then added. Such parts of an expression
which are formed separately first and then added are known as terms. Look at the
expression (4x
2
 – 3xy). We say that it has two terms, 4x
2
 and –3xy. The term 4x
2
 is a
product of 4, x and x, and the term (–3xy) is a product of (–3), x and y.
Terms are added to form expressions. Just as the terms 4x and 5 are added to
form the expression (4x + 5), the terms 4x
2
 and (–3xy) are added to give the expression
(4x
2
 – 3xy). This is because 4x
2
 + (–3xy) = 4x
2
 – 3xy.
Note, the minus sign (–)  is included in the term. In the expression 4x
2
 –3xy, we
took the term as (–3xy) and not as (3xy). That is why we do not need to say that
terms are ‘added or subtracted’ to form an expression; just ‘added’ is enough.
Factors of a term
We saw above that the expression (4x
2
 – 3xy) consists of two terms 4x
2
 and –3xy. The
term 4x
2
 is a product of 4, x and x; we say that 4, x and x are the factors of the term 4x
2
.
A term is a product of its factors. The term –3xy is a product of the factors –3, x and y.
Describe how the
following expressions
are obtained:
7xy + 5, x
2
y, 4x
2
 – 5x
TRY THESE
ALGEBRAIC EXPRESSIONS 231 231 231 231 231
We can represent the terms and factors of
the terms of an expression conveniently and
elegantly by a tree diagram. The tree for the
expression (4x
2
 – 3xy) is as shown in the
adjacent figure.
Note, in the tree diagram, we have used
dotted lines for factors and continuous lines for
terms. This is to avoid mixing them.
Let us draw a tree diagram for the expression
5xy + 10.
The factors are such that they cannot be
further factorised. Thus we do not write 5xy as
5 × xy, because xy can be further factorised.
Similarly , if x
3
 were a term, it would be written as
x × x × x and not x
2
 × x. Also, remember that
1 is not taken as a separate factor.
Coefficients
W e have learnt how to write a term as a product of factors.
One of these factors may be numerical and the others algebraic
(i.e., they contain variables). The numerical factor is said to be
the numerical coefficient or simply the coefficient of the term.
It is also said to be the coefficient of the rest of the term (which
is obviously the product of algebraic factors of the term). Thus
in 5xy, 5 is the coefficient of the term. It is also the coefficient
of xy. In the term 10xyz, 10 is the coefficient of xyz, in the
term –7x
2
y
2
, –7 is the coefficient of x
2
y
2
.
When the coefficient of a term is +1, it is usually omitted.
For example, 1x is written as x; 1 x
2
y
2
 is written as x
2
y
2
 and
so on. Also, the coefficient (–1) is indicated only by the
minus sign. Thus (–1) x is written as – x; (–1) x
2 
y
2
 is
written as – x
2 
y
2
 and so on.
Sometimes, the word ‘coefficient’ is used in a more general way . Thus
we say that in the term 5xy, 5 is the coefficient of xy, x is the coefficient of 5y
and y is the coefficient of 5x. In 10xy
2
, 10 is the coefficient of xy
2
, x is the
coefficient of 10y
2
 and y
2
 is the coefficient of 10x. Thus, in this more general
way , a coefficient may be either a numerical factor or an algebraic factor or
a product of two or more factors. It is said to be the coefficient of the
product of the remaining factors.
EXAMPLE 1 Identify , in the following expressions, terms which are not
constants. Give their numerical coefficients:
xy + 4, 13 – y
2
, 13 – y + 5y
2
, 4p
2
q – 3pq
2
 + 5
TRY THESE
1. What are the terms in the
following expressions?
Show how the terms are
formed. Draw a tree diagram
for each expression:
8y + 3x
2
, 7mn – 4, 2x
2
y.
2. Write three expression each
having 4 terms.
Identify the coefficients
of the terms of following
expressions:
4x – 3y, a + b + 5, 2y + 5, 2xy
TRY THESE
MATHEMATICS 232 232 232 232 232
SOLUTION
S. No. Expression T erm (which is not Numerical
a Constant) Coefficient
(i) xy + 4 xy 1
(ii) 13 – y
2
– y
2
–1
(iii) 13 – y + 5y
2
–y –1
5y
2
5
(iv) 4p
2
q – 3pq
2
 + 5 4p
2
q 4
– 3pq
2
–3
EXAMPLE 2
 (a) What are the coefficients of x in the following expressions?
4x – 3y, 8 – x + y, y
2
x – y, 2z – 5xz
(b) What are the coefficients of  y in the following expressions?
4x – 3y, 8 + yz, yz
2
 + 5, my + m
SOLUTION
 (a) In each expression we look for a term with x as a factor. The remaining part of that
term is the coefficient of x.
S. No. Expression T erm with Factor x Coefficient of x
(i) 4x – 3y 4x 4
(ii) 8 – x + y –x –1
(iii) y
2
x – yy
2
xy
2
(iv) 2z – 5xz – 5xz – 5z
(b) The method is similar to that in (a) above.
S. No. Expression T erm with factor y Coefficient of y
(i) 4x – 3y – 3y –3
(ii) 8 + yz yz z
(iii) yz
2
 + 5 yz
2
z
2
(iv) my + mmy m
12.4  LIKE AND UNLIKE TERMS
When terms have the same algebraic factors, they are like terms. When terms have different
algebraic factors, they are unlike terms. For example, in the expression 2xy – 3x + 5xy – 4,
look at the terms 2xy and 5xy. The factors of 2xy are 2, x and y. The factors of 5xy are 5,
x and y. Thus their algebraic (i.e., those which contain variables) factors are the same and
Page 5


ALGEBRAIC EXPRESSIONS 229 229 229 229 229
12.1  INTRODUCTION
We have already come across simple algebraic expressions like x + 3,  y – 5, 4x + 5,
10y – 5 and so on. In Class VI, we have seen how these expressions are useful in formulating
puzzles and problems. W e have also seen examples of several expressions in the chapter on
simple equations.
Expressions are a central concept in algebra. This Chapter is devoted to algebraic
expressions. When you have studied this Chapter, you will know how algebraic
expressions are formed, how they can be combined, how we can find their values and
how they can be used.
12.2  HOW ARE EXPRESSIONS FORMED?
We now know very well what a variable is. We use letters x, y, l, m, ... etc. to denote
variables. A variable can take various values. Its value is not fixed. On the other hand, a
constant has a fixed value. Examples of constants are: 4, 100, –17, etc.
W e combine variables and constants to make algebraic expressions. For this, we use the
operations of addition, subtraction, multiplication and division. W e have already come across
expressions like 4x + 5, 10y – 20. The expression 4x + 5 is obtained from the variable x, first
by multiplying x by the constant 4 and then adding the constant 5 to the product. Similarly,
10y – 20 is obtained by first multiplying y by 10 and then subtracting 20 from the product.
The above expressions were obtained by combining variables with constants. We can
also obtain expressions by combining variables with themselves or with other variables.
Look at how the following expressions are obtained:
x
2
, 2y
2
, 3x
2
 – 5, xy, 4xy + 7
(i) The expression x
2
 is obtained by multiplying the variable x by itself;
x × x = x
2
Just as 4 × 4 is written as 4
2
, we write x × x = x
2
. It is commonly read as x squared.
Chapter  12
Algebraic
Expressions
MATHEMATICS 230 230 230 230 230
(Later, when you study the chapter ‘Exponents and Powers’ you will realise that x
2
may also be read as x raised to the power 2).
In the same manner, we can write x × x × x = x
3
Commonly, x
3
 is read as ‘x cubed’. Later, you will realise that x
3
 may also be read
as x raised to the power 3.
x, x
2
, x
3
, ... are all algebraic expressions obtained from x.
(ii) The expression 2y
2
 is obtained from y:2y
2
 = 2 × y × y
Here by multiplying y with y we obtain y
2
 and then we multiply y
2
 by the constant 2.
(iii) In (3x
2
 – 5) we first obtain x
2
, and multiply it by 3 to get 3x
2
.
From 3x
2
, we subtract 5 to finally arrive at 3x
2
 – 5.
(iv) In xy, we multiply the variable x with another variable y. Thus,
x × y = xy.
 (v) In 4xy + 7, we first obtain xy, multiply it by 4 to get 4xy and add
7 to 4xy to get the expression.
12.3  TERMS OF AN EXPRESSION
W e shall now put in a systematic form what we have learnt above about how expressions
are formed. For this purpose, we need to understand what terms of an expression and
their factors are.
Consider the expression (4x + 5). In forming this expression, we first formed 4x
separately as a product of 4 and x and then added 5 to it. Similarly consider the expression
(3x
2
 + 7y). Here we first formed 3x
2
 separately as a product of 3, x and x. We then
formed 7y separately as a product of 7 and y. Having formed 3x
2
 and 7y separately, we
added them to get the expression.
Y ou will find that the expressions we deal with can always be seen this way. They
have parts which are formed separately and then added. Such parts of an expression
which are formed separately first and then added are known as terms. Look at the
expression (4x
2
 – 3xy). We say that it has two terms, 4x
2
 and –3xy. The term 4x
2
 is a
product of 4, x and x, and the term (–3xy) is a product of (–3), x and y.
Terms are added to form expressions. Just as the terms 4x and 5 are added to
form the expression (4x + 5), the terms 4x
2
 and (–3xy) are added to give the expression
(4x
2
 – 3xy). This is because 4x
2
 + (–3xy) = 4x
2
 – 3xy.
Note, the minus sign (–)  is included in the term. In the expression 4x
2
 –3xy, we
took the term as (–3xy) and not as (3xy). That is why we do not need to say that
terms are ‘added or subtracted’ to form an expression; just ‘added’ is enough.
Factors of a term
We saw above that the expression (4x
2
 – 3xy) consists of two terms 4x
2
 and –3xy. The
term 4x
2
 is a product of 4, x and x; we say that 4, x and x are the factors of the term 4x
2
.
A term is a product of its factors. The term –3xy is a product of the factors –3, x and y.
Describe how the
following expressions
are obtained:
7xy + 5, x
2
y, 4x
2
 – 5x
TRY THESE
ALGEBRAIC EXPRESSIONS 231 231 231 231 231
We can represent the terms and factors of
the terms of an expression conveniently and
elegantly by a tree diagram. The tree for the
expression (4x
2
 – 3xy) is as shown in the
adjacent figure.
Note, in the tree diagram, we have used
dotted lines for factors and continuous lines for
terms. This is to avoid mixing them.
Let us draw a tree diagram for the expression
5xy + 10.
The factors are such that they cannot be
further factorised. Thus we do not write 5xy as
5 × xy, because xy can be further factorised.
Similarly , if x
3
 were a term, it would be written as
x × x × x and not x
2
 × x. Also, remember that
1 is not taken as a separate factor.
Coefficients
W e have learnt how to write a term as a product of factors.
One of these factors may be numerical and the others algebraic
(i.e., they contain variables). The numerical factor is said to be
the numerical coefficient or simply the coefficient of the term.
It is also said to be the coefficient of the rest of the term (which
is obviously the product of algebraic factors of the term). Thus
in 5xy, 5 is the coefficient of the term. It is also the coefficient
of xy. In the term 10xyz, 10 is the coefficient of xyz, in the
term –7x
2
y
2
, –7 is the coefficient of x
2
y
2
.
When the coefficient of a term is +1, it is usually omitted.
For example, 1x is written as x; 1 x
2
y
2
 is written as x
2
y
2
 and
so on. Also, the coefficient (–1) is indicated only by the
minus sign. Thus (–1) x is written as – x; (–1) x
2 
y
2
 is
written as – x
2 
y
2
 and so on.
Sometimes, the word ‘coefficient’ is used in a more general way . Thus
we say that in the term 5xy, 5 is the coefficient of xy, x is the coefficient of 5y
and y is the coefficient of 5x. In 10xy
2
, 10 is the coefficient of xy
2
, x is the
coefficient of 10y
2
 and y
2
 is the coefficient of 10x. Thus, in this more general
way , a coefficient may be either a numerical factor or an algebraic factor or
a product of two or more factors. It is said to be the coefficient of the
product of the remaining factors.
EXAMPLE 1 Identify , in the following expressions, terms which are not
constants. Give their numerical coefficients:
xy + 4, 13 – y
2
, 13 – y + 5y
2
, 4p
2
q – 3pq
2
 + 5
TRY THESE
1. What are the terms in the
following expressions?
Show how the terms are
formed. Draw a tree diagram
for each expression:
8y + 3x
2
, 7mn – 4, 2x
2
y.
2. Write three expression each
having 4 terms.
Identify the coefficients
of the terms of following
expressions:
4x – 3y, a + b + 5, 2y + 5, 2xy
TRY THESE
MATHEMATICS 232 232 232 232 232
SOLUTION
S. No. Expression T erm (which is not Numerical
a Constant) Coefficient
(i) xy + 4 xy 1
(ii) 13 – y
2
– y
2
–1
(iii) 13 – y + 5y
2
–y –1
5y
2
5
(iv) 4p
2
q – 3pq
2
 + 5 4p
2
q 4
– 3pq
2
–3
EXAMPLE 2
 (a) What are the coefficients of x in the following expressions?
4x – 3y, 8 – x + y, y
2
x – y, 2z – 5xz
(b) What are the coefficients of  y in the following expressions?
4x – 3y, 8 + yz, yz
2
 + 5, my + m
SOLUTION
 (a) In each expression we look for a term with x as a factor. The remaining part of that
term is the coefficient of x.
S. No. Expression T erm with Factor x Coefficient of x
(i) 4x – 3y 4x 4
(ii) 8 – x + y –x –1
(iii) y
2
x – yy
2
xy
2
(iv) 2z – 5xz – 5xz – 5z
(b) The method is similar to that in (a) above.
S. No. Expression T erm with factor y Coefficient of y
(i) 4x – 3y – 3y –3
(ii) 8 + yz yz z
(iii) yz
2
 + 5 yz
2
z
2
(iv) my + mmy m
12.4  LIKE AND UNLIKE TERMS
When terms have the same algebraic factors, they are like terms. When terms have different
algebraic factors, they are unlike terms. For example, in the expression 2xy – 3x + 5xy – 4,
look at the terms 2xy and 5xy. The factors of 2xy are 2, x and y. The factors of 5xy are 5,
x and y. Thus their algebraic (i.e., those which contain variables) factors are the same and
ALGEBRAIC EXPRESSIONS 233 233 233 233 233
hence they are like terms. On the other hand the
terms 2xy and –3x, have different algebraic factors.
They are unlike terms. Similarly, the terms, 2xy
and 4, are unlike terms. Also, the terms –3x and 4
are unlike terms.
12.5 MONOMIALS, BINOMIALS, TRINOMIALS AND
POLYNOMIALS
An expression with only one term is called a monomial; for example, 7xy, – 5m,
3z
2
, 4 etc.
An expression which contains two unlike terms is called a
binomial; for example, x + y, m – 5, mn + 4m, a
2
 – b
2
 are
binomials. The expression 10pq is not a binomial; it is a
monomial. The expression (a + b + 5) is not a binomial.
It contains three terms.
An expression which contains three terms is called a
trinomial; for example, the expressions x + y + 7, ab + a +b,
3x
2
 – 5x + 2, m + n + 10 are trinomials. The expression
ab + a + b + 5 is, however not a trinomial; it contains four
terms and not three. The expression x +  y + 5x is not a trinomial as the terms x and 5x are
like terms.
In general, an expression with one or more terms is called a polynomial. Thus a
monomial, a binomial and a trinomial are all polynomials.
EXAMPLE 3 State with reasons, which of the following pairs of terms are of like
terms and which are of unlike terms:
(i) 7x, 12y (ii) 15x, –21x (iii) – 4ab, 7ba (iv) 3xy, 3x
(v) 6xy
2
, 9x
2
y (vi) pq
2
, – 4pq
2
(vii) mn
2
, 10mn
SOLUTION
S. Pair Factors Algebraic Like/ Remarks
No. factors same Unlike
or different terms
(i) 7x 7, x Different Unlike The variables in the
12y 12, y terms are different.
(ii) 15x 15, x Same Like
–21x –21, x
(iii) – 4ab – 4, a, b Same Like Remember
7 ba 7, a, bab = ba
TRY THESE
Group the like terms together from the
following:
12x, 12, – 25x, – 25, – 25y, 1, x, 12y, y
TRY THESE
Classify the following
expressions as a monomial,
a binomial or a trinomial: a,
a + b, ab + a + b, ab + a
+ b – 5, xy, xy + 5,
5x
2 
– x + 2, 4pq – 3q + 5p,
7, 4m – 7n + 10, 4mn + 7.