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Class 8 NCERT Solutions – Chapter 9 Algebraic Expressions and Identities – Exercise 9.2

  • Last Updated : 05 Nov, 2020

Question 1. Find the product of the following pairs of monomials.

Monomial: Expression containing only one term

(i) 4, 7p 

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Ans: 



 (4) * (7p) = 28p

 (ii) -4p, 7p

Ans:   

(-4p) * (7p)  = -28p2

Explanation: When a negative number is multiplied to a positive number the product becomes negative.

(iii) -4p, 7pq

Ans:   

(-4p) * (7pq)  = -28p2q

(iv) 4p3, -3p

Ans:  

(4p3) * (-3p) = -12p4

(v) 4p, 0

Ans:    

(4p) * (0) = 0 

Explanation: Any number when multiplied to zero (0) gives zero.

Question 2. Find the areas of rectangles with the following pairs of monomials as their lengths and breadths respectively.

           (p, q); (10m, 5n); (20x2, 5y2); (4x, 3x2); (3mn, 4np)

Note: Area of rectangle is the product of length and breadth [length * breadth]

Ans: 

         For (p,q):



                       p * q = pq 

         For (10m, 5n):

                      10m *  5n = 50mn

         For (20x2,5y2):

                       20x2 * 5y2 = 100x2y2

         For (4x,3x2):

                         4x * 3x2 = 12x3

         For (3mn, 4np): 

                         3mn * 4np = 12mn2p

Question 3. Complete the table of products.

Ans:  



First monomial 

Second monomial  

  2x-5y3x-4xy7x2y-9x2y2
           2x4x2-10xy6x3-8x2y14x3y-18x3y2
          -5y-10xy25y2-15x2y20xy2-35x2y245x2y3
          3x26x3-15x2y9x4-12x3y21x4y-27x4y2
         -4xy-8x2y20xy2-12x3y16x2y2-28x3y236x3y3
          7x2y14x3y-35x2y221x4y-28x3y249x4y2-63x4y3
        -9x2y2-18x3y245x2y3-27x4y236x3y363x4y381x4y4

Question 4. Obtain the volume of rectangular boxes with the following length, breadth, and height respectively.

Note: The volume of the rectangle is the product of length, breadth, height [length * breadth * height]

(i) 5a, 3a2, 7a4

Ans: 

 5a * 3a2 * 7a4 = 105a7

(ii) 2p , 4q , 8r

Ans: 

2p * 4q * 8r = 64pqr

(iii) xy, 2x2y, 2xy2



Ans:  

xy * 2x2y * 2xy2 = 4x4y4

(iv) a, 2b, 3c

Ans:  a * 2b * 3c = 6abc

Question 5. Obtain the product of 

(i) xy, yz, zx

Ans: 

xy * yz * zx = x2y2z2

(ii) a, -a2, a3

Ans: 

a * -a2 * a3 = -a6

(iii) 2, 4y, 8y2, 16y3

Ans:

2 * 4y * 8y2 * 16y3 = 1024y6

(iv) a, 2b, 3c, 6abc

Ans: 

a * 2b * 3c * 6abc = 36a2b2c2

(v) m, -mn, mnp

Ans:

m * -mn * mnp = -m3n2p

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