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NCERT Exemplar · Class 8 · Maths

Chapter 7: Algebraic Expressions and Identities & Factorisation

Practice each question, then open the answer or worked solution.

Questions

44 questions
Q1Written answer

The product of a monomial and a binomial is a

(a) monomial (b) binomial

(c) trinomial (d) none of these

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Worked solution

Solution:-

(b) binomial

Let monomial = 2x, binomial = x + y

Then, product of a monomial and a binomial = (2x) × (x + y)

= 2x2 + 2xy

Q2Written answer

In a polynomial, the exponents of the variables are always

(a) integers (b) positive integers

(c) non-negative integers (d) non-positive integers

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Worked solution

Solution:-

(b) positive integers

Q3Written answer

Which of the following is correct?

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

(c) (a – b)2 = a2 – b2 (d) (a + b)2 = a2 + 2ab – b2

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Worked solution

Solution:-

(b) (a – b)2 = a2 – 2ab + b2

We have, = (a – b) × (a – b)

= a × (a – b) – b × (a – b)

= a2 – ab – ba + b2

= a2 – 2ab + b2

Q4Written answer

The sum of –7pq and 2pq is

(a) –9pq (b) 9pq (c) 5pq (d) – 5pq

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Worked solution

Solution:-

(d) – 5pq

The given two monomials are like terms.

Then sum of -7pq and 2pg = – 7pq + 2pq

= (-7 + 2) pq

= -5pq

Q5Written answer

If we subtract –3x2y2 from x2y2, then we get

(a) – 4x2y2 (b) – 2x2y2 (c) 2x2y2 (d) 4x2y2

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Worked solution

Solution:-

(d) 4x2y2

We have,

The given two monomials are like terms.

Subtract –3x2y2 from x2y2 = x2y2 – (- 3x2y2)

= x2y2 + 3x2y2

= x2y2 (1 + 3)

= 4x2y2

Q6Written answer

Like term as 4m3n2 is

(a) 4m2n2 (b) – 6m3n2 (c) 6pm3n2 (d) 4m3n

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Worked solution

Solution:-

(b) – 6m3n2

Like terms are formed from the same variables, and the powers of these variables are also the same. But coefficients of like terms need not be the same.

Q7Written answer

Which of the following is a binomial?

(a) 7 × a + a (b) 6a2 + 7b + 2c

(c) 4a × 3b × 2c (d) 6 (a2 + b)

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Worked solution

Solution:-

(d) 6 (a2 + b)

Expressions that contain exactly two terms are called binomials.

= 6 (a2 + b)

= 6a2 + b

Q8Written answer

Sum of a – b + ab, b + c – bc and c – a – ac is

(a) 2c + ab – ac – bc (b) 2c – ab – ac – bc

(c) 2c + ab + ac + bc (d) 2c – ab + ac + bc

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Worked solution

Solution:-

(a) 2c + ab – ac – bc

We have,

= (a – b + ab) + (b + c – bc) + (c – a – ac)

= a – b + ab + b + c – bc + c – a – ac

Now, grouping like terms

= (a – a) + (-b + b) + (c + c) + ab – bc – ac

= 2c + ab – bc – ac

Q9Written answer

Product of the following monomials 4p, – 7q3, –7pq is

(a) 196 p2q4 (b) 196 pq4 (c) – 196 p2q4 (d) 196 p2q3

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Worked solution

Solution:-

(a) 196 p2q4

= 4p × (– 7q3) × (–7pq)

= (4 × (-7) × (-7)) × p × q3 × pq

= 196p2q4

Q10Written answer

Area of a rectangle with length 4ab and breadth 6b2 is

(a) 24a2b2 (b) 24ab3 (c) 24ab2 (d) 24ab

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Worked solution

Solution:-

(b) 24ab3

We know that the area of a rectangle = length × breadth

Given, length = 4ab, breadth = 6b2

= 4ab × 6b2

= 24ab3