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CBSE Important Questions for Class 8 Maths Algebraic Expressions and Identities - 2025-26

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Algebraic Expressions and Identities Class 8 Extra Questions and Answers Free PDF Download

CBSE Class 8 Maths Chapter 8 Algebraic Expressions and Identities explains algebra, where you'll learn how to work with terms, factors, and coefficients, and master operations like addition, subtraction, and multiplication of algebraic expressions. Important identities are covered in-depth, helping you simplify and solve problems effortlessly.


Based on the CBSE Class 8 Maths Syllabus, this chapter emphasizes simplifying algebraic expressions, applying standard identities, and solving real-world problems. These Class 8 Maths Important Questions cover key topics to help you revise effectively and understand the core concepts of algebraic expressions. Practice these questions to strengthen your concepts and score high in exams!

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Access Class 8 Maths Chapter 8: Algebraic Expressions and Identities Important Questions

Very Short Answer Questions (1 Mark)

1. Identify the coefficient of x in the expression

(a) 1 

(b) -1 

(c) -2 

(d) None of these

Ans: Given: \[x\]

We need to find the coefficient of the given expression.

We know that coefficient is the number before any variable. 

So, the expression \[x\] can be written as $ 1\times x $ . 

So, the coefficient will be $ 1. $ 


2. The expression for sum of numbers p and q subtracted from their product is

(a) p+q-pq  

(b) pq-p+q  

(c)  pq-(p+q)  

(d)  pq+p-q  

Ans: Given: variables $ p,q $ 

To find: the expression for sum of numbers $ p $ and $ q $ subtracted from their product

The product of the numbers will be

$ \begin{align} & p\times q \\ & =pq \\ \end{align} $

Sum of numbers will be

 $ p+q $ 

Therefore, the required answer will be

$pq-(p+q) $ 


3. Sum of \[\mathbf{ab,}\] \[\mathbf{a\text{ }+\text{ }b,}\] and \[\mathbf{b\text{ }+\text{ }ab}\] is

(a) 2ab+2a+b

(b)2ab+2b

(c)2ab+a+b

(d)2ab+a+2b

Ans: Given: $ab, a+b, b+ab $ 

We need to find the sum of the given terms.

Therefore, the sum will be

$ \begin{align} & ab+a+b+b+ab \\ & =2ab+a+2b \\ \end{align} $


4. The value of expression $ \mathbf{5{{x}^{2}}-2} $ when $\mathbf{ x=3 }$ is

 (a)-12 

 (b) 8 

 (c) 43 

 (d) 36 

Ans: Given: $ 5{{x}^{2}}-2 $ , $ x=3 $ 

We need to find the value of $ 5{{x}^{2}}-2 $ at $ x=3 $ 

We will put $ 3 $ in place of $ x $ in the expression $ 5{{x}^{2}}-2 $ 

Therefore, the value of the expression will be

$ \begin{align} & 5{{x}^{2}}-2 \\ & =5{{(3)}^{2}}-2 \\ & =5(3)-2 \\ & =45-2 \\ & =43 \\ \end{align} $


5. On simplifying the result is $\mathbf{ (a+b-2)-(b-a+2)+(a-b+2)} $

 (a) $\mathbf{ a-b+2} $ 

 (b) $ \mathbf{a-b-2 }$ 

 (c) $ \mathbf{3a-b-2 }$ 

 (d) $\mathbf{ 3a+b+2 }$ 

Ans: Given: $ (a+b-2)-(b-a+2)+(a-b+2) $ 

We need to simplify the given expression.

So, the expression will be simplified as

$ \begin{align} & (a+b-2)-(b-a+2)+(a-b+2) \\ & =a+b-2-b+a-2+a-b+2 \\ & =3a-b-2 \\ \end{align} $


6. What is the statement for the expression $\mathbf{ 2(y-9)} $ 

 (a)  2y  subtracted from  9  

 (b)  9  subtracted from  y  and multiplied by  2  

 (c)  9  subtracted from  9  

 (d) Three of  y  minus  9 $ 

Ans: Given: $ 2(y-9) $ 

We need to find the statement of the given expression.

We can write the expression as $ 9 $ subtracted from $ y $ and multiplied by $ 2 $.


7. The factors of $\mathbf{ 7{{a}^{2}}+14a} $ is

 (a) $ \mathbf{7(a+2) }$ 

 (b) $\mathbf{ 21a } $ 

 (c) $ \mathbf{7(a+1) }$ 

 (d) $\mathbf{ 7a(a+2) }$ 

Ans: Given: $ 7{{a}^{2}}+14a $ 

We need to factorize the given expression

The factors of $ 7{{a}^{2}}+14a $ will be

 $ 7{{a}^{2}}+14a $ 

Take $ 7a $ as a common factor, we get

 $ 7a(a+2) $ 

Therefore, these will be the factors of the given expression.


Short Answer Questions (2 Mark)

8. The volume of a rectangular box where length, breadth, and height are $ \mathbf{2a,4b,8c} $ respectively.

Ans: Given: length of rectangular box, $ l=2a $ 

Breadth of rectangular box, $ b=4b $ 

Height of rectangular box, $ h=8c $ 

We need to find the volume of the rectangular box with given dimensions.

We know, Volume of a cuboid $ =l\times b\times h $ 

Therefore, the volume of the rectangular box will be

$ \begin{align} & =2a\times 4b\times 8c \\ & =64abc \\ \end{align} $


9. Simplify $\mathbf{ (p+{{q}^{2}})({{p}^{2}}-q) } $ 

Ans: Given: $ (p+{{q}^{2}})({{p}^{2}}-q) $ 

We need to simplify the given expression.

To simplify, we will open the brackets by multiplying the terms in it with each other.

Therefore, the expression will become

\[\begin{align} & \left( p+{{q}^{2}} \right)\left( {{p}^{2}}-q \right) \\ & =p\left( {{p}^{2}}-q \right)+{{q}^{2}}\left( {{p}^{2}}-q \right) \\ & ={{p}^{3}}-pq+{{q}^{2}}{{p}^{2}}-{{q}^{3}} \\ \end{align}\]


10. If $ \mathbf{pq=3 } $ and $\mathbf{ p+q=6, } $ then $\mathbf{ ({{p}^{2}}+{{q}^{2}})} $ is

Ans: Given: $ pq=3 $ , $ p+q=6, $ 

We need to find $ ({{p}^{2}}+{{q}^{2}}) $ 

We know that, 

$ \begin{align} & {{(p+q)}^{2}}={{p}^{2}}+{{q}^{2}}+2pq \\ & \left( {{p}^{2}}+{{q}^{2}} \right)={{(p+q)}^{2}}-2pq \\ \end{align} $

Substituting the values, $ pq=3 $ , $ p+q=6, $ in above equation we get

$ \begin{align} & \left( {{p}^{2}}+{{q}^{2}} \right) \\ & ={{(6)}^{2}}-2(3) \\ & =36-6 \\ & =30 \\ \end{align} $


11. Simplify $\mathbf{ x(2x-1)+5 }$ and find its value at $ \mathbf{x=-3} $ 

Ans: Given: $ x(2x-1)+5 $ 

We need to find the value of the given expression at $ x=-3 $ 

We will substitute $ x=-3 $ in the given expression. Therefore, the expression after simplifying will be

$ \begin{align} & 2{{(-3)}^{2}}-(-3)+5 \\ & =2(9)+3+5 \\ & =18+8 \\ & =26 \\ \end{align} $


Short Answer Questions (3 Mark)

12. Find the value of $ \mathbf{{{\left( \frac{2}{3}x-\frac{3}{2}y \right)}^{2}}+2xy }$ 

Ans: Given: $ {{\left( \frac{2}{3}x-\frac{3}{2}y \right)}^{2}}+2xy $ 

We need to find the value of the given expression

We know that, $ {{(a-b)}^{2}}={{a}^{2}}+{{b}^{2}}-2ab $ 

Therefore, using the formula, we will get the value of the expression as:

\[\begin{align} & ={{\left( \frac{2}{3} \right)}^{2}}{{x}^{2}}+{{\left( \frac{3}{2} \right)}^{2}}{{y}^{2}}-2\left( \frac{2}{3} \right)x\left( \frac{3}{2} \right)y+2xy \\ & =\frac{4}{9}{{x}^{2}}+\frac{9}{4}{{y}^{2}}-2xy+2xy \\ & =\frac{4}{9}{{x}^{2}}+\frac{9}{4}{{y}^{2}} \\ \end{align}\]


13. Find $\mathbf{ (m+n)(m-n)\left( {{m}^{2}}+{{n}^{2}} \right)\left( {{m}^{4}}+{{n}^{4}} \right)} $ 

Ans: Given: $ (m+n)(m-n)\left( {{m}^{2}}+{{n}^{2}} \right)\left( {{m}^{4}}+{{n}^{4}} \right) $ 

We need to simplify the given expression. 

Formula Used: $ (a+b)(a-b)={{a}^{2}}-{{b}^{2}} $ 

Simplifying the expression, we get

$ \begin{align} & (m+n)(m-n)\left( {{m}^{2}}+{{n}^{2}} \right)\left( {{m}^{4}}+{{n}^{4}} \right) \\ & =\left( {{m}^{2}}-{{n}^{2}} \right)\left( {{m}^{2}}+{{n}^{2}} \right)\left( {{m}^{4}}+{{n}^{4}} \right) \\ & =\left[ {{\left( {{m}^{2}} \right)}^{2}}-{{\left( {{n}^{2}} \right)}^{2}} \right]\left( {{m}^{4}}+{{n}^{4}} \right) \\ & =\left[ {{m}^{4}}-{{n}^{4}} \right]\left[ {{m}^{4}}+{{n}^{4}} \right] \\ & ={{m}^{8}}-{{n}^{8}} \\ \end{align} $


14. From the sum of $\mathbf{ 3a-b+9} $ and $\mathbf{ -b-9} $ , subtract $\mathbf{ 3a-b-9} $ 

Ans: Given: expressions $ 3a-b+9 $ , $ -b-9 $ , $ 3a-b-9 $ 

We need to subtract $ 3a-b-9 $ from the sum of $ 3a-b+9 $ and $ -b-9 $ 

The sum of the first two terms, $ -b-9 $ and $ 3a-b+9 $ will be

$ \begin{align} & 3a-b+9+(-b-9) \\ & =3a-b+9-b-9 \\ & =3a-2b \\ \end{align} $

Now subtracting $ 3a-b+9 $ from $ 3a-2b $ , we get

$ \begin{align} & 3a-2b-(3a-b-9) \\ & =3a-2b-3a+b=9 \\ & =-b+9 \\ \end{align} $


15. Find $ \mathbf{194\times 206 }$ using suitable identity

Ans: Given: $ 194\times 206 $ 

We need to find the value of the given expression using an identity.

We can write,

$ \begin{align} & 194=(200-6) \\ & 206=(200+6) \\ \end{align} $

Using identity, $ (a-b)(a+b)={{a}^{2}}-{{b}^{2}} $ , the given expression can be simplified as:

$ \begin{align} & (200-6)(200+6) \\ & ={{(200)}^{2}}-{{(6)}^{2}} \\ & =40000-36 \\ & =39964 \\ \end{align} $


16. If $\mathbf{ x+\frac{1}{x}=9, }$ find the value of $\mathbf{ \left( {{x}^{2}}+\frac{1}{{{x}^{2}}} \right). }$ 

Ans: Given: $ x+\frac{1}{x}=9 $ 

To find: $ \left( {{x}^{2}}+\frac{1}{{{x}^{2}}} \right) $ 

Let $ x+\frac{1}{x}=9\text{ }..............(1) $ 

Square both sides, we will get

$ \begin{align} & \left( {{x}^{2}}+\frac{1}{{{x}^{2}}} \right)={{(9)}^{2}} \\ & \left( {{x}^{2}}+\frac{1}{{{x}^{2}}} \right)=81 \\ \end{align} $

Now, we know that $ {{(a+b)}^{2}}={{a}^{2}}+{{b}^{2}}+2ab $ 

So,

$ \begin{align} & {{\left( x+\frac{1}{x} \right)}^{2}}={{x}^{2}}+{{\left( \frac{1}{x} \right)}^{2}}+2x\times \frac{1}{x} \\ & {{\left( x+\frac{1}{x} \right)}^{2}}={{x}^{2}}+\frac{1}{{{x}^{2}}}+2 \\ & 81={{x}^{2}}+\frac{1}{{{x}^{2}}}+2 \\ & {{x}^{2}}+\frac{1}{{{x}^{2}}}=81-2 \\ & {{x}^{2}}+\frac{1}{{{x}^{2}}}=79 \\ \end{align} $


17. Simplify $\mathbf{ \left( {{x}^{2}}-3x+2 \right)(5x-2)-\left( 3{{x}^{2}}+4x-5 \right)(2x-1) }$ 

Ans: Given: $ \left( {{x}^{2}}-3x+2 \right)(5x-2)-\left( 3{{x}^{2}}+4x-5 \right)(2x-1) $ 

We need to simplify the given expression.

First simplifying, $ \left( {{x}^{2}}-3x+2 \right)(5x-2), $ we will get

$ \begin{align} & \left( {{x}^{2}}-3x+2 \right)(5x-2) \\ & =5{{x}^{3}}-15{{x}^{2}}+10x-2{{x}^{2}}+6x-4 \\ & =5{{x}^{3}}-17{{x}^{2}}+16x-4\text{ }...................(1) \\ \end{align} $

Now simplifying, $ \left( 3{{x}^{2}}+4x-5 \right)(2x-1) $ , we will get

$ \begin{align} & \left( 3{{x}^{2}}+4x-5 \right)(2x-1) \\ & =6{{x}^{3}}+8{{x}^{2}}-10x-3{{x}^{2}}-4x+5 \\ & =6{{x}^{3}}+5{{x}^{2}}-14x+5\text{ }..................(2) \\ \end{align} $

Subtract $ (1)-(2) $ to get the result

$ \begin{align} & \left( {{x}^{2}}-3x+2 \right)(5x-2)-\left( 3{{x}^{2}}+4x-5 \right)(2x-1) \\ & =5{{x}^{3}}-17{{x}^{2}}+16x-4-\left[ 6{{x}^{3}}+5{{x}^{2}}-14x+5 \right] \\ & =5{{x}^{3}}-17{{x}^{2}}+16x-4-6{{x}^{3}}-5{{x}^{2}}+14x-5 \\ & =-{{x}^{3}}-22{{x}^{2}}+30x-9 \\ \end{align} $


18. Find the following product $\mathbf{ (a-3b)(a+3b)\left( {{a}^{2}}+9{{b}^{2}} \right) }$ 

Ans: Given: $ (a-3b)(a+3b)\left( {{a}^{2}}+9{{b}^{2}} \right) $ 

We need to find the product of the given expression.

Formula Used: $ (a-b)(a+b)={{a}^{2}}-{{b}^{2}} $ 

Solve the given expression using the identity, we will get

$ \begin{align} & (a-3b)(a+3b)\left( {{a}^{2}}+9{{b}^{2}} \right) \\ & =\left[ {{(a)}^{2}}-{{(3b)}^{2}} \right]\left( {{a}^{2}}+9{{b}^{2}} \right) \\ & =\left( {{a}^{2}}-9{{b}^{2}} \right)\left( {{a}^{2}}+9{{b}^{2}} \right) \\ & ={{\left( {{a}^{2}} \right)}^{2}}-{{\left( 9{{b}^{2}} \right)}^{2}} \\ & ={{a}^{4}}-81{{b}^{4}} \\ \end{align} $


Long Answer Questions (5 Mark)

19. Find $\mathbf{ {{(3st+4t)}^{2}}-{{(3st-4t)}^{2}} }$ 

Ans: Given: $ {{(3st+4t)}^{2}}-{{(3st-4t)}^{2}} $ 

We need to simplify the given expression.

We know that,

$ \begin{align} & {{(a+b)}^{2}}={{a}^{2}}+{{b}^{2}}+2ab \\ & \therefore {{(3st+4t)}^{2}}={{(3st)}^{2}}+{{(4t)}^{2}}+2(3st)(4t) \\ & =9{{s}^{2}}{{t}^{2}}+16{{t}^{2}}+24s{{t}^{2}}.................(1) \\ \end{align} $

We also know that,

$ \begin{align} & {{(a-b)}^{2}}={{a}^{2}}+{{b}^{2}}-2ab \\ & \therefore {{(3st-4t)}^{2}}={{(3st)}^{2}}+{{(4t)}^{2}}-2(3st)(4t) \\ & {{(3st-4t)}^{2}}=9{{s}^{2}}{{t}^{2}}+16{{t}^{2}}-24s{{t}^{2}}............(2) \\ \end{align} $

Therefore, using equations $ (1) $ and $ (2) $ , the given expression will become

$ \begin{align} & =9{{s}^{2}}{{t}^{2}}+16{{t}^{2}}+24s{{t}^{2}}-\left[ 9{{s}^{2}}{{t}^{2}}+16{{t}^{2}}-24s{{t}^{2}} \right] \\ & =9{{s}^{2}}{{t}^{2}}+16{{t}^{2}}+24s{{t}^{2}}-9{{s}^{2}}{{t}^{2}}-16{{t}^{2}}+24s{{t}^{2}} \\ & =48s{{t}^{2}} \\ \end{align} $


20. The area of a rectangle is uv where u is length and v is breadth. If the length of rectangle is increased by \[\mathbf{5\text{ units}}\] and breadth is decreased by \[\mathbf{3\text{ units}\text{.}}\]. The new area of rectangle is?

Ans: Given: Area of the old rectangle $ =uv $ 

Length of the old rectangle $ =u $ 

Breadth of told rectangle $ =v $ 

Length of the ew rectangle $ =u+5 $ 

Breadth of the new rectangle $ =v-3 $ 

We need to find the area of the new rectangle.

We know that, Area of rectangle $ =length\times breadth $ 

Therefore, the area of the new rectangle will be 

$ \begin{align} & =(u+5)(v-3) \\ & =uv-3u+5v-15 \\ \end{align} $


21. If \[\mathbf{\left( {{x}^{2}}+\frac{1}{{{x}^{2}}} \right)=27}\], find $\mathbf{ x-\frac{1}{x} }$ 

Ans: Given: \[\left( {{x}^{2}}+\frac{1}{{{x}^{2}}} \right)=27\]

We need to find $ x-\frac{1}{x} $
Use identity, $ {{(a-b)}^{2}}={{a}^{2}}+{{b}^{2}}-2ab $ 

Substitute, $ a=x,b=\frac{1}{x} $ , we get

$ \begin{align} & {{\left( x-\frac{1}{x} \right)}^{2}}={{x}^{2}}+\frac{1}{{{x}^{2}}}-2x\times \frac{1}{x} \\ & \Rightarrow {{\left( x-\frac{1}{x} \right)}^{2}}={{x}^{2}}+\frac{1}{{{x}^{2}}}-2 \\ \end{align} $

We know that, \[\left( {{x}^{2}}+\frac{1}{{{x}^{2}}} \right)=27\], therefore,

$ \begin{align} & \Rightarrow {{\left( x-\frac{1}{x} \right)}^{2}}=27-2 \\ & \Rightarrow {{\left( x-\frac{1}{x} \right)}^{2}}=25 \\ & \Rightarrow \left( x-\frac{1}{x} \right)=\sqrt{25} \\ & \Rightarrow \left( x-\frac{1}{x} \right)=5 \\ \end{align} $


22. Simplify using identity, $\mathbf{ \frac{2.3\times 2.3-0.3\times 0.3}{2.3\times 2.3-2\times 2.3\times 0.3+0.3\times 0.3} }$ 

Ans: Given: 0 $ \frac{2.3\times 2.3-0.3\times 0.3}{2.3\times 2.3-2\times 2.3\times 0.3+0.3\times 0.3} $ 

We need to simplify the given expression using an identity.

Identity used: 

$ \begin{align} & 1.{{a}^{2}}-{{b}^{2}}=(a+b)(a-b) \\ & 2.{{(a-b)}^{2}}={{a}^{2}}+{{b}^{2}}-2ab \\ \end{align} $

Using these identities, the given expression can be written as:

$ \begin{align} & =\frac{2.3\times 2.3-0.3\times 0.3}{2.3\times 2.3-2\times 2.3\times 0.3+0.3\times 0.3} \\ & =\frac{{{(2.3)}^{2}}-{{(0.3)}^{2}}}{{{(2.3)}^{2}}-2(2.3)(0.3)+{{(0.3)}^{2}}} \\ & =\frac{(2.3+0.3)(2.3-0.3)}{{{(2.3-0.3)}^{2}}} \\ & =\frac{(2.3+0.3)}{(2.3-0.3)} \\ & =\frac{2.6}{2} \\ & =1.3 \\ \end{align} $


23. The sum of \[\mathbf{\left( x\text{ }+\text{ }3 \right)}\] observations is $\mathbf{ ({{x}^{4}}-81).} $ Find the mean of the observations.

Ans: Given: 

Number of observations $ =\left( x\text{ }+\text{ }3 \right) $ 

Sum of observations $ =({{x}^{4}}-81) $ 

We know that $ \text{Mean=}\frac{\text{Sum of all observations}}{\text{Total number of observations}} $ 

Therefore, mean of the observations will be

$ \begin{align} & =\frac{\left( {{x}^{4}}-81 \right)}{(x+3)} \\ & =\frac{{{x}^{4}}-{{3}^{4}}}{x+3} \\ & =\frac{{{\left( {{x}^{2}} \right)}^{2}}-{{\left( {{3}^{2}} \right)}^{2}}}{(x+3)} \\ \end{align} $

We know that, $ {{a}^{2}}-{{b}^{2}}=(a+b)(a-b) $ 

$ \begin{align} & =\frac{\left( {{x}^{2}}+{{3}^{2}} \right)\left( {{x}^{2}}-{{3}^{2}} \right)}{(x+3)} \\ & =\frac{\left( {{x}^{2}}+{{3}^{2}} \right)(x-3)(x+3)}{(x+3)} \\ & =\left( {{x}^{2}}+9 \right)(x-3) \\ & ={{x}^{3}}+9x-3{{x}^{2}}-27 \\ & ={{x}^{3}}-3{{x}^{2}}+9x-27 \\ \end{align} $


24. Abhishek is \[\mathbf{6}\] years older than Jagadish. Six years ago Abhishek was twice as old as Jagadish. Write down the situation in algebraic expression and find how old is each now?

Ans: Given: Age of Abhishek \[=6\] years older than Jagadish

Six years ago Abhishek age $ =2 $ times of Jagadish age

We need to write the algebraic expression and find the age of both.

Let, present age of Jagadish $ =x $ 

Abhishek is \[6\] years older than Jagadish. 

Therefore, age of Abhishek $ =x+6 $ 

Jagadish age \[6\] years ago $ =x-6 $

Age of Abhishek \[6\] years ago $ =(x+6)-6 $ 

According to the question, Six years ago Abhishek was twice as old as Jagadish. So,

$ \begin{align} & (x+6)-6=2(x-6) \\ & \Rightarrow x+6-6=2x-12 \\ & \Rightarrow -x=-12 \\ & \Rightarrow x=12 \\ \end{align} $

We can conclude that present age of Jagadish $ =12\text{ years} $ 

The present age of Abhishek will be

$ \begin{align} & =x+6 \\ & =18\text{ years} \\ \end{align} $


25. Rohit mother gave him $ \mathbf{\text{Rs}\text{. }4x{{y}^{2}} }$ and his father gave him Rs. $\mathbf{ (5x{{y}^{2}}+3) }$ . Out of this total money he spent Rs. $\mathbf{ (10-3x{{y}^{2}}) }$ on his birthday party. How much money is left with him?

Ans: Given: Mother gives Rohit amount $ =4x{{y}^{2}} $ 

Father gives Rohit amount $ =(5x{{y}^{2}}+3) $ 

Total amount spent by Rohit $ =(10-3x{{y}^{2}}) $ 

We need to find how much money is left with him.

Total Amount Received by Rohit is,

$ \begin{align} & =4x{{y}^{2}}+(5x{{y}^{2}}+3) \\ & =9x{{y}^{2}}+3 \\ \end{align} $

Total amount spent by Rohit is

 $ =(10-3x{{y}^{2}}) $ 

Therefore, Amount left with him will be

$ \begin{align} & =\left( 9x{{y}^{2}}+3 \right)-\left( 10-3x{{y}^{2}} \right) \\ & =9x{{y}^{2}}+3-10+3x{{y}^{2}} \\ & =12x{{y}^{2}}-7 \\ \end{align} $


How the Chapter 8 Maths Class 8 Important Questions Are Going to Help Students 

The chapter 8 class 8 important questions are going to help the students immensely because-


  • These solutions provide step-by-step explanations helping the students to answer questions better.

  • These solutions contain a list of important formulas that will help the students remember them during exam time.

  • The questions and solutions are written based on the current syllabus.

  • These questions and solutions will further help students during competitive exam revisions.

  • Questions are compiled by experts who have in-depth knowledge about the subject.


7 Important Formulas from Class 8 Maths Chapter 8 Algebraic Expressions and Identities

S.No.

Formulas

1.

(a + b)2 = a2 + 2ab + b2

2.

(a – b)2 = a2 – 2ab + b2

3.

a2 – b2 = (a – b)(a + b)

4.

(a + b)3 = a3 + b3 + 3ab(a + b)

5.

(a – b)3 = a3 – b3 – 3ab(a – b) 

6.

a3 – b3 = (a – b)(a2 + ab + b2)

7.

a3 + b3 = (a + b)(a2 – ab + b2)



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Conclusion 

CBSE Class 8 Maths Chapter 8 Algebraic Expressions and Identities Important Questions are essential for learning this crucial topic. They help students understand key concepts like terms, factors, coefficients, and operations on algebraic expressions. Practising these questions ensures a solid grasp of standard identities, which are vital for solving problems efficiently. These questions not only prepare students for exams but also strengthen their foundational skills in algebra. By solving them regularly, students can boost their confidence, improve accuracy, and score well in their exams with ease.


Related Study Materials for CBSE Class 8 Maths Chapter 8



CBSE Class 8 Maths Chapter-wise Important Questions



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FAQs on CBSE Important Questions for Class 8 Maths Algebraic Expressions and Identities - 2025-26

1. Why is practising important questions for CBSE Class 8 Maths Chapter 8 essential for the 2025-26 exams?

Practising important questions for Algebraic Expressions and Identities is crucial because it helps students focus on the most frequently asked topics and question patterns. This targeted practice ensures a better understanding of concepts like applying standard identities and simplifying complex expressions, which often carry significant marks in the exam. It also builds confidence and improves problem-solving speed for the 2025-26 session.

2. Which topics in Algebraic Expressions and Identities are most important for exams?

For the Class 8 Maths exam, the most important topics from this chapter that are frequently tested include:

  • Multiplication of polynomials, especially a binomial by a trinomial.
  • Application of the four standard identities: (a+b)², (a-b)², (a+b)(a-b), and (x+a)(x+b).
  • Simplifying expressions that involve a combination of addition, subtraction, and multiplication.
  • Questions that require using identities to calculate products or squares of numerical values.

3. What are the four standard algebraic identities that I must know for Class 8 Maths?

The four standard algebraic identities, as per the CBSE syllabus, are essential for solving many problems quickly. They are:

  • (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
Mastering the application of these identities is key to scoring well on questions from this chapter.

4. How can using an algebraic identity be more efficient than direct multiplication in an exam?

Using an algebraic identity is a strategic shortcut that saves valuable time and reduces calculation errors. For example, to calculate 104 × 96, direct multiplication is slow. By representing it as (100 + 4)(100 - 4) and applying the identity (a+b)(a-b) = a² - b², the answer is found instantly as 100² - 4² = 10000 - 16 = 9984. This method is faster and less prone to mistakes under exam pressure.

5. What is a common mistake students make when subtracting algebraic expressions?

A very common error is mishandling the negative sign when subtracting one polynomial from another. For instance, in a question asking to subtract (3a - 2b) from (7a + 5b), students often forget to change the sign of every term in the expression being subtracted. The correct method is (7a + 5b) - (3a - 2b) = 7a + 5b - 3a + 2b. Forgetting to change -2b to +2b is a frequent source of incorrect answers in exams.

6. What kind of Higher-Order Thinking Skills (HOTS) questions are asked from this chapter?

HOTS questions from Algebraic Expressions and Identities often involve multiple steps or real-world applications. An expected question might be to find the area of a rectangular park whose length and breadth are given as algebraic expressions (e.g., length = 3x+4, breadth = 3x-2). This requires you to first multiply the binomials and then simplify. Another HOTS type involves using identities in reverse to find missing terms or to factorise an expression.

7. How are questions on 'multiplication of polynomials' typically framed in exams?

Questions on this topic can be framed in several ways:

  • Direct Multiplication: Asking to find the product of a binomial and a trinomial, for example, (2x + 3) (x² - 4x + 5).
  • Simplification: Asking to simplify a long expression involving addition, subtraction, and multiplication, which tests your ability to manage signs and combine like terms correctly.
  • Verification: Asking you to multiply expressions and then verify the result by substituting a numerical value for the variable.

8. Why is it so important to correctly identify 'like terms' before adding or subtracting?

Correctly identifying and combining like terms (terms with identical variables and exponents) is the most fundamental rule in simplifying expressions. It is the mathematical equivalent of grouping similar objects before counting. If you incorrectly add unlike terms, such as adding 4x² and 7x, the entire foundation of your calculation becomes wrong. Every subsequent step will be incorrect, making this a critical skill for avoiding zero marks on complex simplification problems.