Syllabus of Class 8 Mathematics
1.Rational Numbers2.Linear Equations in one variable3.Understanding Quadrilaterals4.Practical Geometry5.Data Handling6.Squares Square Roots7.Cube and Cube Roots8.Comparing Quantities9.Algebraic Expressions and Identities10.Visualising Solid Shapes11.Mensuration12.Exponents and Powers13.Direct and Inverse Properties14.Factorisation15.Introduction to Graph16.Playing with Numbers
Algebraic Expressions and Identities Class 8 Solutions
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Class 8 Maths Chapter 9 Notes - Algebric Expressions And Identities
Introduction to Algebraic expressions and identities
An algebraic expression is made up of constants, variables, and mathematical operations (addition, subtraction, multiplication and/or division). A constant is number whose value does not change, whereas the value of a variable changes. For example, x + 9 is an algebraic expression where 9 is a constant and x is a variable. Different elements like terms, factors and coefficients form these expressions.
Each part of an algebraic expression separated by a plus or minus sign is called a term of the algebraic expression.
Factors are the numbers and/or variables whose product make a term. If we look at the term 7x, it is the product of two factors 7 and x.
Coefficient is defined as the number that is multiplied by the other variables. In the term 11pqr, 11 is the coefficient of pqr.
An expression can be termed as monomial, binomial, trinomial, and polynomial based on the number of terms it has.
Monomial: It is an algebraic expression with only one term. For example, 9y is a monomial.
Binomial: It is an algebraic expression with two terms. For example, 2a – 6b is a binomial.
Trinomial: It is an algebraic expression with three terms. For example, 9a + 5b – c .
Polynomial: It is an algebraic expression that contains one or more terms consisting of constants and/or variables (whose exponents are non-negative integers). Monomials, binomials and trinomials come under the category of polynomials.
The terms of an algebraic expression can be categorised as like terms and unlike terms.
Like and Unlike Terms
Like Terms: If two or more terms have the same variable, then they are called like terms.
For example, 7x + 8x is an algebraic expression with like terms.
Unlike Terms: If two or more terms have different variables, they are called unlike terms.
For example, 7x + 8y is an algebraic expression with unlike terms.
We should understand how to select like and unlike terms because this helps us to add or subtract the terms of an algebraic expression. Let us see how we can do this.
NCERT Solutions for Class 8 Maths Chapter 9 |
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Addition and Subtraction |
While adding and subtracting two or more algebraic expressions, we first group the like terms. Then we add or subtract them using simple number rules.
If a and b are coefficients and x and y are variables, ax + bx + y = (a + b)x + y.
If a and b are coefficients and x and y are variables, ax − bx + y = (a − b)x + y.
Let us see an example.
Subtract x2 + 3y2 + 4xy – 4xyz from 9x2 – 4y2 + 7y + 2xy + 6.
9x2 – 4y2 + 7y + 2xy + 6
x2 + 3y2 + 4xy – 4xyz
– – – +
---------------------------------------------------
8x2 – 7y2 + 7y − 2xy + 6 + 4xyz
Multiplication
While multiplying algebraic expressions, every term of the first expression is multiplied with every term of the second expression. We have to follow some other steps as well.
Multiplying Like Terms
● The coefficients of the terms will get multiplied.
● The powers of the variables will not get multiplied, but added.
● Example: The product of 4x2 and 9x will be 36x3.
Multiplying Unlike Terms
● The coefficients of the terms will get multiplied.
● The power will remain the same if the variables are different.
● If some of the variables are the same, then their powers will be added.
● Example: The product of xy, 4x, and 9xz will be 36x3yz.
Let’s see the multiplication of different types of algebraic expressions
Monomial by Monomial: If a and b are coefficients and x and y are variables, ax × bxy = abx2y.
Monomial by Binomial: If a and b are coefficients and x and y are variables, ax × (x + bxy) = ax2+ abx2y.
Monomial by Trinomial: If a and b are coefficients and x, y, and z are variables, ax × (x + by – z) = ax2+ abxy – axz.
Binomial by Binomial: If a and b are coefficients and x, y, and z are variables, (ax + y) × (x – z) = ax2– axz + xy − yz.
Binomial by Trinomial: If a and b are coefficients and x, y, and z are variables, (ax + y) × (x + by – z) = ax2+ abxy – axz.
Let us see an example.
Find the value of (p + 2q + r) × (2p – 3q).
(p + 2q + r) × (2p – 3q) = p (2p – 3q) + 2q (2p – 3q) + r (2p – 3q)
(p + 2q + r) × (2p – 3q) = p × 2p – p × 3q + 2q × 2p – 3q × 2q + r × 2p – r × 3q
(p + 2q + r) × (2p – 3q) = 2p2 – 3pq + 4pq – 6q2 + 2pr – 3qr
(p + 2q + r) × (2p – 3q) = 2p2 + pq – 6q2 + 2pr – 3qr
Equations contain an ‘equal to’ operator along with some other expressions. In an equation, if for every value of the variable, the value of the expression on the LHS is equal to the value of the expression on the RHS, then the equation is an identity. We will learn four standard identities that we generally use.
● (a + b)2 = a2 + 2ab + b2
● (a – b)2 = a2 – 2ab + b2
● (a + b)(a – b) = a2 – b2
● (x + a)(x + b) = x2 + (a + b)x + ab
Let us see an example where identities are used.
Find the value of (4x2 + 4xy) (4x2 + 3xy).
Using the identity: (x + a) (x + b) = x2 + (a + b) x + ab
(4x2 + 4xy) (4x2 + 3xy)
= (4x2)2 + (4xy + 3xy)(4x2) + 4xy × 3xy
= 16x4 + (16x3y + 12x3y) + 12x2y2
= 16x4 + 28x3y + 12x2y2
****************************************†**
*(a + b)2 = a2 + 2ab + b2
(a - b)2 = a2 - 2ab + b2
(a + b)(a - b) = a2 - b2
(x + a)(x + b) = x2 + (a + b)x + ab
(x + a)(x - b) = x2 + (a - b)x - ab
(x - a)(x + b) = x2 + (b - a)x - ab
(x - a)(x - b) = x2 - (a + b)x + ab
(a + b)3 = a3 + b3 + 3ab(a + b)
(a - b)3 = a3 - b3 - 3ab(a - b)
Question: 1 Give five examples of expressions containing one variable and five examples of expressions containing two variables.
Answer:
Five examples of expressions containing one variable are:
Five examples of expressions containing two variables are:
Question: 2(i) Show on the number line.
Answer:
x on the number line:
Question: 2(ii)
Show on the number line
Answer:
x-4 on the number line:
Question: 2(iii) Show on the number line
2x+1
Answer:
2x+1 on the number line:
Question: 2(iv) Show on the number line
Answer:
3x - 2 on the number line
Algebraic expressions and identities class 8 solutions - Topic 9.2 Terms, Factors and Coefficients
Question:1.Identify the coefficients of each term in the expression.
Answer:
coefficient of each term are given below
Algebraic expressions and identities class 8 ncert solutions - Topic 9.3 Monomials, Binomials and Polynomials
Question: 1(i). Classify the following polynomials as monomials, binomials and trinomials.
Answer:
Binomial since there are two terms with non zero coefficients.
Question: 1(ii) Classify the following polynomials as monomials, binomials and trinomials.
Answer:
Trinomial since there are three terms with non zero coefficients.
Question:1(iii) Classify the following polynomials as monomials, binomials and trinomials.
Answer:
Trinomial since there are three terms with non zero coefficients.
Question: 1(iv) Classify the following polynomials as monomials, binomials and trinomials.
Answer:
Binomial since there are two terms with non zero coefficients.
Question: 1(v) Classify the following polynomials as monomials, binomials and trinomials.
Answer:
Monomial since there is only one term.
Question: 2(b) constant 3 binomials with and as variables;
Answer:
Three binomials with x and y as variables are:
Question: 2(c) constant 3 monomials with and as variables;
Answer:
Three monomials with x and y as variables are
NCERT Solutions for Class 8 Maths Chapter 9 Algebraic Expressions and Identities Topic 9.4 Like and Unlike Terms
Question:(i) Write two terms which are like
Answer:
Question:(ii) Write two terms which are like
Answer:
we can write more like terms
Question:(iii) Write two terms which are like
Answer:
NCERT Solutions for Class 8 Maths Chapter 9 Algebraic Expressions and Identities - Exercise: 9.1
Question:1(i) Identify the terms , their coefficients, for each of the following expressions
Answer
following are the terms and coefficient
The terms are and the coefficients are 5 and -3.
Question: 1(ii) Identify the terms , their coefficients, for each of the following expressions
Answer:
the following is the solution
Question:1(iii)Identify the terms , their coefficients, for each of the following expressions
Answer:
Question: 1(iv) Identify the terms , their coefficients, for each of the following expressions
Answer:
The terms are 3, -pq, qr,and -rp and the coefficients are 3, -1, 1 and -1 respectively.
Question:1(v) Identify the terms , their coefficients, for each of the following expressions
Answer:
Above are the terms and coefficients
Question: 1(vi) Identify the terms , their coefficients, for each of the following expressions
Answer:
The terms are 0.3a, -0.6ab and 0.5b and the coefficients are 0.3, -0.6 and 0.5.
Question: 2(a) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
Binomial.
Question: 2(b) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
Monomial.
Question: 2(c) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
This polynomial does not fit in any of these three categories.
Question: 2(d)Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
Trinomial.
Question: 2(e) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
Binomial.
Question: 2(f) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
Trinomial.
Question: 2(g) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
Trinomial.
Question: 2(h) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
Binomial.
Question: 2(i) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
This polynomial does not fit in any of these three categories.
Question:2(j) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
Monomial.
Question: 2(k) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
Binomial.
Question: 2(i) Classify the following polynomials as monomials, binomials,trinomi.Which polynomials do not fit any of these categories?
Answer:
Binomial.
Question: 3(i) Add the following
Answer:
ab-bc+bc-ca+ca-ab=0.
Question:3 (ii) Add the following
Answer:
Question:3 (ii)Add the following
Answer:
Question: 3(iv)Add the following
Answer:
Question:1FindFirst find and multiply it by ; or first find and multiply it by .
Answer:
We observe that the result is same in both cases and the result does not depend on the order in which multiplication has been carried out.
Class 8 maths chapter 9 question answer - exercise: 9.2
Question: 1(i) Find the product of the following pairs monomials
Answer:
Question: 1(ii) Find the product of the following pairs monomials
Answer:
Question: 1(iii) Find the product of the following pairs monomials
Answer:
Question: 1(iv) Find the product of the following pairs monomials
Answer:
Question:1(v) Find the product of the following pairs monomials
Answer:
Question:2(A) Find the areas of rectangles with the followin pairs of monomials as their lengths and breadth respectively.
Answer:
The question can be solved as follows
Question:2(B)Find the areas of rectangles with the followin pairs of monomials as their lengths and breadth respectivi.
Answer:
the area is calculated as follows
Question:2(C) Find the areas of rectangles with the followin pairs of monomials as their lengths and breadth respectivi.
Answer:
the following is the solution
Question:2(D) Find the areas of rectangles with the followin pairs of monomials as their lengths and breadth respectivi.
Answer:
area of rectangles is
Question:2(E) Find the areas of rectangles with the followin pairs of monomials as their lengths and breadth respectivi.
Answer:
The area is calculated as follows
Question:3
Complete the table.
First monomial Second monomial | ||||||
... | ... | ... | ... | ... | ||
... | ... | ... | ... | ... | ||
... | ... | ... | ... | ... | ... | |
... | ... | ... | ... | ... | ... | |
... | ... | ... | ... | ... | ... | |
... | ... | ... | ... | ... | ... |
Answer:
First monomial Second monomial | ||||||
Question:4(i) Obtain the volume of rectangular boxes with the following length, breadth and height respectfully.
Answer:
Question:4(ii)Obtain the volume of rectangular boxes with the following length, breadth and height respectfully.
Answer:
the volume of rectangular boxes with the following length, breadth and height is
Question:4(iii) Obtain the volume of rectangular boxes with the following length, breadth and height respectfully.
Answer:
the volume of rectangular boxes with the following length, breadth and height is
Question:4(iv) Obtain the volume of rectangular boxes with the following length, breadth and height respectfully.
Answer:
the volume of rectangular boxes with the following length, breadth and height is
Question:5(i) Obtain the product of
Answer:
the product
Question:5(ii)Obtain the product of
Answer:
the product
Question:5(iii)Obtain the product of
Answer:
the product
Question:5(iv) Obtain the product of
Answer:
the product
Question:5(v) Obtain the product of
Answer:
the product
Class 8 maths chapter 9 NCERT solutions - Topic 9.8.1 Multiplying a Monomial by a Binomial
Question:(i) Obtain the product of
Answer:
Using distributive law,
Question:(ii)Obtain the product of
Answer:
Using distributive law,
We have :
NCERT Solutions for Class 8 Maths Chapter 9 Algebraic Expressions and Identities - Topic 9.8.2 Multiplying A Monomial By A Trinomial
Question:1Obtain the product of
Answer:
By using distributive law,
Class 8 maths chapter 9 NCERT solutions - exercise: 9.3
Question:1(i) Carry out the multiplication of the expressions in each of the following pairs
Answer:
Multiplication of the given expression gives :
By distributive law,
Question1(Ii)Carry out the multiplication of the expressions in each of the following pairs
Answer:
We have ab, (a-b).
Using distributive law we get,
Question:1(iii) Carry out the multiplication of the expressions in each of the following pairs
Answer:
Using distributive law we can obtain multiplication of given expression:
Question:1(iv) Carry out the multiplication of the expressions in each of the following pairs
Answer:
We will obtain multiplication of given expression by using distributive law :
Question:1(v) Carry out the multiplication of the expressions in each of the following pairs
Answer:
Using distributive law :
Question:2 Complete the table
First expression | Second expression | Product | |
(i) | ... | ||
(ii) | ... | ||
(iii) | ... | ||
(iv) | ... | ||
(v) | ... |
Answer:
We will use distributive law to find product in each case.
First expression | Second expression | Product | |
(i) | |||
(ii) | |||
(iii) | |||
(iv) | |||
(v) |
Question:3(i) Find the product
Answer:
Opening brackets :
or
Question:3(ii) Find the product
Answer:
We have,
Question:3(iii) Find the product
Answer:
We have
Question:3(iv) Find the product
Answer:
We have
or
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Nice article,sir, from which city do you belong?
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