NCERT Exemplar Solutions
Class 9 - Mathematics
CHAPTER 2: POLYNOMIALS

Meaning of a Polynomial, Degree of a polynomial, Coefficients, Monomials, Binomials etc., Constant, Linear, Quadratic Polynomials etc., Value of a polynomial for a given value of the variable, Zeroes of a polynomial, Remainder theorem, Factor theorem, Factorisation of a quadratic polynomial by splitting the middle term, Factorisation of algebraic expressions by using the Factor theorem, Algebraic identities

Exercise 2.1 - Multiple Choice Questions

Write the correct answer in each of the following:

Question.  1

Which one of the following is a polynomial?

(A)

\(\dfrac{x^2}{2} - \dfrac{2}{x^2}\)

(B)

\(\sqrt{2x} - 1\)

(C)

\(x^2 + \dfrac{3x^{3/2}}{\sqrt{x}}\)

(D)

\(\dfrac{x-1}{x+1}\)

Question.  2

\(\sqrt{2}\) is a polynomial of degree

(A)

2

(B)

0

(C)

1

(D)

\(\dfrac{1}{2}\)

Question.  3

Degree of the polynomial \(4x^4 + 0x^3 + 0x^5 + 5x + 7\) is

(A)

4

(B)

5

(C)

3

(D)

7

Question.  4

Degree of the zero polynomial is

(A)

0

(B)

1

(C)

Any natural number

(D)

Not defined

Question.  5

If \(p(x)=x^2-2\sqrt{2}\,x+1\), then \(p(2\sqrt{2})\) is equal to

(A)

0

(B)

1

(C)

\(4\sqrt{2}\)

(D)

\(8\sqrt{2}+1\)

Question.  6

The value of the polynomial \(5x-4x^2+3\), when \(x=-1\), is

(A)

-6

(B)

6

(C)

2

(D)

-2

Question.  7

If \(p(x)=x+3\), then \(p(x)+p(-x)\) is equal to

(A)

3

(B)

\(2x\)

(C)

0

(D)

6

Question.  8

Zero of the zero polynomial is

(A)

0

(B)

1

(C)

Any real number

(D)

Not defined

Question.  9

Zero of the polynomial \(p(x)=2x+5\) is

(A)

\(-\dfrac{2}{5}\)

(B)

\(-\dfrac{5}{2}\)

(C)

\(\dfrac{2}{5}\)

(D)

\(\dfrac{5}{2}\)

Question.  10

One of the zeroes of the polynomial \(2x^2+7x-4\) is

(A)

2

(B)

\(\dfrac{1}{2}\)

(C)

\(-\dfrac{1}{2}\)

(D)

-2

Question.  11

If \(x^{51}+51\) is divided by \(x+1\), the remainder is

(A)

0

(B)

1

(C)

49

(D)

50

Question.  12

If \(x+1\) is a factor of the polynomial \(2x^2+kx\), then the value of \(k\) is

(A)

-3

(B)

4

(C)

2

(D)

-2

Question.  13

\(x+1\) is a factor of the polynomial

(A)

\(x^3+x^2-x+1\)

(B)

\(x^3+x^2+x+1\)

(C)

\(x^4+x^3+x^2+1\)

(D)

\(x^4+3x^3+3x^2+x+1\)

Question.  14

One of the factors of \((25x^2-1)+(1+5x)^2\) is

(A)

\(5+x\)

(B)

\(5-x\)

(C)

\(5x-1\)

(D)

\(10x\)

Question.  15

The value of \(249^2-248^2\) is

(A)

\(1^2\)

(B)

477

(C)

487

(D)

497

Question.  16

The factorisation of \(4x^2+8x+3\) is

(A)

\((x+1)(x+3)\)

(B)

\((2x+1)(2x+3)\)

(C)

\((2x+2)(2x+5)\)

(D)

\((2x-1)(2x-3)\)

Question.  17

Which of the following is a factor of \((x+y)^3-(x^3+y^3)\)?

(A)

\(x^2+y^2+2xy\)

(B)

\(x^2+y^2-xy\)

(C)

\(xy^2\)

(D)

\(3xy\)

Question.  18

The coefficient of \(x\) in the expansion of \((x+3)^3\) is

(A)

1

(B)

9

(C)

18

(D)

27

Question.  19

If \(\dfrac{x}{y}+\dfrac{y}{x}=-1\) \((x, y \ne 0)\), the value of \(x^3-y^3\) is

(A)

1

(B)

-1

(C)

0

(D)

\(\dfrac{1}{2}\)

Question.  20

If \(49x^2-b=(7x+\dfrac{1}{2})(7x-\dfrac{1}{2})\), then the value of \(b\) is

(A)

0

(B)

\(\dfrac{1}{\sqrt{2}}\)

(C)

\(\dfrac{1}{4}\)

(D)

\(\dfrac{1}{2}\)

Question.  21

If \(a+b+c=0\), then \(a^3+b^3+c^3\) is equal to

(A)

0

(B)

\(abc\)

(C)

\(3abc\)

(D)

\(2abc\)

Exercise 2.2

Question. 1

Which of the following expressions are polynomials? Justify your answer:

(i) \(8\)

(ii) \(\sqrt{3}x^2 - 2x\)

(iii) \(1 - \sqrt{5}x\)

(iv) \(\dfrac{1}{5x^{-2}} + 5x + 7\)

(v) \(\dfrac{(x-2)(x-4)}{x}\)

(vi) \(\dfrac{1}{x+1}\)

(vii) \(\dfrac{1}{7}a^3 - \dfrac{2}{\sqrt{3}}a^2 + 4a - 7\)

(viii) \(\dfrac{1}{2x}\)

Answer:

Polynomials: (i), (ii), (iv), (vii) because the exponent of the variable after simplification in each of these is a whole number.

Question. 2

Write whether the following statements are True or False. Justify your answer.

(i) A binomial can have at most two terms

(ii) Every polynomial is a binomial

(iii) A binomial may have degree 5

(iv) Zero of a polynomial is always 0

(v) A polynomial cannot have more than one zero

(vi) The degree of the sum of two polynomials each of degree 5 is always 5.

Answer:

(i) False, because a binomial has exactly two terms.

(ii) False, \(x^3 + x + 1\) is a polynomial but not a binomial.

(iii) True, because a binomial is a polynomial whose degree is a whole number \(\ge 1\), so degree can be 5 also.

(iv) False, because zero of a polynomial can be any real number.

(v) False, a polynomial can have any number of zeroes. It depends upon the degree of the polynomial.

(vi) False, \(x^5 + 1\) and \(-x^5 + 2x + 3\) are two polynomials of degree 5 but the degree of the sum of the two polynomials is 1.

Exercise 2.3: Short Answer Questions

Question. 1

Classify the following polynomials as polynomials in one variable, two variables etc.:

(i) \(x^2 + x + 1\)

(ii) \(y^3 - 5y\)

(iii) \(xy + yz + zx\)

(iv) \(x^2 - 2xy + y^2 + 1\)

Answer:

(i) One variable

(ii) One variable

(iii) Three variable

(iv) Two variables

Question. 2

Determine the degree of each of the following polynomials:

(i) \(2x - 1\)

(ii) \(-10\)

(iii) \(x^3 - 9x + 3x^5\)

(iv) \(y^3(1 - y^4)\)

Answer:

(i) 1

(ii) 0

(iii) 5

(iv) 7

Question. 3

For the polynomial \(\dfrac{x^3 + 2x + 1}{5} - \dfrac{7}{2}x^2 - x^6\), write:

(i) the degree of the polynomial

(ii) the coefficient of \(x^3\)

(iii) the coefficient of \(x^6\)

(iv) the constant term

Answer:

(i) 6

(ii) \(\dfrac{1}{5}\)

(iii) \(-1\)

(iv) \(\dfrac{1}{5}\)

Question. 4

Write the coefficient of \(x^2\) in each of the following:

(i) \(\dfrac{\pi}{6}x + x^2 - 1\)

(ii) \(3x - 5\)

(iii) \((x - 1)(3x - 4)\)

(iv) \((2x - 5)(2x^2 - 3x + 1)\)

Answer:

(i) 1

(ii) 0

(iii) 3

(iv) \(-16\)

Question. 5

Classify the following as a constant, linear, quadratic and cubic polynomials:

(i) \(2 - x^2 + x^3\)

(ii) \(3x^3\)

(iii) \(5t - \sqrt{7}\)

(iv) \(4 - 5y^2\)

(v) \(3\)

(vi) \(2 + x\)

(vii) \(y^3 - y\)

(viii) \(1 + x + x^2\)

(ix) \(t^2\)

(x) \(\sqrt{2}x - 1\)

Answer:

Constant Polynomial : (v)

Linear Polynomials : (iii), (vi), (x)

Quadratic Polynomials : (iv), (viii), (ix)

Cubic Polynomials : (i), (ii), (vii)

Question. 6

Give an example of a polynomial, which is:

(i) monomial of degree 1

(ii) binomial of degree 20

(iii) trinomial of degree 2

Answer:

(i) \(10x\)

(ii) \(x^{20} + 1\)

(iii) \(2x^2 - x - 1\)

Question. 7

Find the value of the polynomial \(3x^3 - 4x^2 + 7x - 5\), when \(x = 3\) and also when \(x = -3\).

Answer:

61, \(-143\)

Question. 8

If \(p(x) = x^2 - 4x + 3\), evaluate: \(p(2) - p(-1) + p\left(\dfrac{1}{2}\right)\).

Answer:

\(-\dfrac{31}{4}\)

Question. 9

Find \(p(0)\), \(p(1)\), \(p(-2)\) for the following polynomials:

(i) \(p(x) = 10x - 4x^2 - 3\)

(ii) \(p(y) = (y + 2)(y - 2)\)

Answer:

(i) \(-3, 3, -39\)

(ii) \(-4, -3, 0\)

Question. 10

Verify whether the following are True or False:

(i) \(-3\) is a zero of \(x - 3\)

(ii) \(-\dfrac{1}{3}\) is a zero of \(3x + 1\)

(iii) \(-\dfrac{4}{5}\) is a zero of \(4 - 5y\)

(iv) 0 and 2 are the zeroes of \(t^2 - 2t\)

(v) \(-3\) is a zero of \(y^2 + y - 6\)

Answer:

(i) False

(ii) True

(iii) False

(iv) True

(v) True

Question. 11

Find the zeroes of the polynomial in each of the following:

(i) \(p(x) = x - 4\)

(ii) \(g(x) = 3 - 6x\)

(iii) \(q(x) = 2x - 7\)

(iv) \(h(y) = 2y\)

Answer:

(i) 4

(ii) \(\dfrac{1}{2}\)

(iii) \(\dfrac{7}{2}\)

(iv) 0

Question. 12

Find the zeroes of the polynomial: \(p(x) = (x - 2)^2 - (x + 2)^2\).

Answer:

0

Question. 13

By actual division, find the quotient and the remainder when the first polynomial is divided by the second polynomial: \(x^4 + 1\); \(x - 1\).

Answer:

\(x^3 + x^2 + x + 1\), 2

Question. 14

By Remainder Theorem find the remainder, when \(p(x)\) is divided by \(g(x)\), where:

(i) \(p(x) = x^3 - 2x^2 - 4x - 1\), \(g(x) = x + 1\)

(ii) \(p(x) = x^3 - 3x^2 + 4x + 50\), \(g(x) = x - 3\)

(iii) \(p(x) = 4x^3 - 12x^2 + 14x - 3\), \(g(x) = 2x - 1\)

(iv) \(p(x) = x^3 - 6x^2 + 2x - 4\), \(g(x) = 1 - \dfrac{3}{2}x\)

Answer:

(i) 0

(ii) 62

(iii) \(\dfrac{3}{2}\)

(iv) \(-\dfrac{136}{27}\)

Question. 15

Check whether \(p(x)\) is a multiple of \(g(x)\) or not:

(i) \(p(x) = x^3 - 5x^2 + 4x - 3\), \(g(x) = x - 2\)

(ii) \(p(x) = 2x^3 - 11x^2 - 4x + 5\), \(g(x) = 2x + 1\)

Answer:

(i) No

(ii) No

Question. 16

Show that:

(i) \(x + 3\) is a factor of \(69 + 11x - x^2 + x^3\)

(ii) \(2x - 3\) is a factor of \(x + 2x^3 - 9x^2 + 12\)

Question. 17

Determine which of the following polynomials has \(x - 2\) a factor:

(i) \(3x^2 + 6x - 24\)

(ii) \(4x^2 + x - 2\)

Answer:

(i)

Question. 18

Show that \(p - 1\) is a factor of \(p^{10} - 1\) and also of \(p^{11} - 1\).

Question. 19

For what value of \(m\) is \(x^3 - 2mx^2 + 16\) divisible by \(x + 2\)?

Answer:

1

Question. 20

If \(x + 2a\) is a factor of \(x^5 - 4a^2x^3 + 2x + 2a + 3\), find \(a\).

Answer:

\(\dfrac{3}{2}\)

Question. 21

Find the value of \(m\) so that \(2x - 1\) be a factor of \(8x^4 + 4x^3 - 16x^2 + 10x + m\).

Answer:

\(-2\)

Question. 22

If \(x + 1\) is a factor of \(ax^3 + x^2 - 2x + 4a - 9\), find the value of \(a\).

Answer:

2

Question. 23

Factorise:

(i) \(x^2 + 9x + 18\)

(ii) \(6x^2 + 7x - 3\)

(iii) \(2x^2 - 7x - 15\)

(iv) \(84 - 2r - 2r^2\)

Answer:

(i) \((x + 6)(x + 3)\)

(ii) \((3x - 1)(2x + 3)\)

(iii) \((x - 5)(2x + 3)\)

(iv) \(2(7 + r)(6 - r)\)

Question. 24

Factorise:

(i) \(2x^3 - 3x^2 - 17x + 30\)

(ii) \(x^3 - 6x^2 + 11x - 6\)

(iii) \(x^3 + x^2 - 4x - 4\)

(iv) \(3x^3 - x^2 - 3x + 1\)

Answer:

(i) \((x - 2)(x + 3)(2x - 5)\)

(ii) \((x - 1)(x - 2)(x - 3)\)

(iii) \((x + 1)(x - 2)(x + 2)\)

(iv) \((x - 1)(x + 1)(3x - 1)\)

Question. 25

Using suitable identity, evaluate the following:

(i) \(103^3\)

(ii) \(101 \times 102\)

(iii) \(999^2\)

Answer:

(i) 1092727

(ii) 10302

(iii) 998001

Question. 26

Factorise the following:

(i) \(4x^2 + 20x + 25\)

(ii) \(9y^2 - 66yz + 121z^2\)

(iii) \(\left(2x + \dfrac{1}{3}\right)^2 - \left(x - \dfrac{1}{2}\right)^2\)

Answer:

(i) \((2x + 5)^2\)

(ii) \((3y - 11z)^2\)

(iii) \(\left(3x - \dfrac{1}{6}\right)\left(x + \dfrac{5}{6}\right)\)

Question. 27

Factorise the following:

(i) \(9x^2 - 12x + 3\)

(ii) \(9x^2 - 12x + 4\)

Answer:

(i) \(3(x - 1)(3x - 1)\)

(ii) \((3x - 2)(3x - 2)\)

Question. 28

Expand the following:

(i) \((4a - b + 2c)^2\)

(ii) \((3a - 5b - c)^2\)

(iii) \((-x + 2y - 3z)^2\)

Answer:

(i) \(16a^2 + b^2 + 4c^2 - 8ab - 4bc + 16ac\)

(ii) \(9a^2 + 25b^2 + c^2 - 30ab + 10bc - 6ac\)

(iii) \(x^2 + 4y^2 + 9z^2 - 4xy - 12yz + 6xz\)

Question. 29

Factorise the following:

(i) \(9x^2 + 4y^2 + 16z^2 + 12xy - 16yz - 24xz\)

(ii) \(25x^2 + 16y^2 + 4z^2 - 40xy + 16yz - 20xz\)

(iii) \(16x^2 + 4y^2 + 9z^2 - 16xy - 12yz + 24xz\)

Answer:

(i) \((3x + 2y - 4z)(3x + 2y - 4z)\)

(ii) \((-5x + 4y + 2z)(-5x + 4y + 2z)\)

(iii) \((4x - 2y + 3z)(4x - 2y + 3z)\)

Question. 30

If \(a + b + c = 9\) and \(ab + bc + ca = 26\), find \(a^2 + b^2 + c^2\).

Answer:

29

Question. 31

Expand the following:

(i) \((3a - 2b)^3\)

(ii) \(\left(\dfrac{1}{x} + \dfrac{y}{3}\right)^3\)

(iii) \(\left(4 - \dfrac{1}{3x}\right)^3\)

Answer:

(i) \(27a^3 - 54a^2b + 36ab^2 - 8b^3\)

(ii) \(\dfrac{1}{x^3} + \dfrac{y}{x^2} + \dfrac{y^2}{3x} + \dfrac{y^3}{27}\)

(iii) \(64 - \dfrac{16}{x} + \dfrac{4}{3x^2} - \dfrac{1}{27x^3}\)

Question. 32

Factorise the following:

(i) \(1 - 64a^3 - 12a + 48a^2\)

(ii) \(8p^3 + \dfrac{12}{5}p^2 + \dfrac{6}{25}p + \dfrac{1}{125}\)

Answer:

(i) \((1 - 4a)(1 - 4a)(1 - 4a)\)

(ii) \(\left(2p + \dfrac{1}{5}\right)\left(2p + \dfrac{1}{5}\right)\left(2p + \dfrac{1}{5}\right)\)

Question. 33

Find the following products:

(i) \(\left(\dfrac{x}{2} + 2y\right)\left(\dfrac{x^2}{4} - xy + 4y^2\right)\)

(ii) \((x^2 - 1)(x^4 + x^2 + 1)\)

Answer:

(i) \(\dfrac{x^3}{8} + 8y^3\)

(ii) \(x^6 - 1\)

Question. 34

Factorise:

(i) \(1 + 64x^3\)

(ii) \(a^3 - 2\sqrt{2}b^3\)

Answer:

(i) \((1 + 4x)(1 - 4x + 16x^2)\)

(ii) \((a - \sqrt{2}b)(a^2 + \sqrt{2}ab + 2b^2)\)

Question. 35

Find the following product: \((2x - y + 3z)(4x^2 + y^2 + 9z^2 + 2xy + 3yz - 6xz)\).

Answer:

\(8x^3 - y^3 + 27z^3 + 18xyz\)

Question. 36

Factorise:

(i) \(a^3 - 8b^3 - 64c^3 - 24abc\)

(ii) \(2\sqrt{2}a^3 + 8b^3 - 27c^3 + 18\sqrt{2}abc\)

Answer:

(i) \((a - 2b - 4c)(a^2 + 4b^2 + 16c^2 + 2ab - 8bc + 4ac)\)

(ii) \((\sqrt{2}a + 2b - 3c)(2a^2 + 4b^2 + 9c^2 - 2\sqrt{2}ab + 6bc + 3\sqrt{2}ac)\)

Question. 37

Without actually calculating the cubes, find the value of:

(i) \(\left(\dfrac{1}{2}\right)^3 + \left(\dfrac{1}{3}\right)^3 - \left(\dfrac{5}{6}\right)^3\)

(ii) \((0.2)^3 - (0.3)^3 + (0.1)^3\)

Answer:

(i) \(-\dfrac{5}{12}\)

(ii) -0.018

Question. 38

Without finding the cubes, factorise:

\((x - 2y)^3 + (2y - 3z)^3 + (3z - x)^3\)

Answer:

\(3(x - 2y)(2y - 3z)(3z - x)\)

Question. 39

Find the value of:

(i) \(x^3 + y^3 - 12xy + 64\), when \(x + y = -4\)

(ii) \(x^3 - 8y^3 - 36xy - 216\), when \(x = 2y + 6\)

Answer:

(i) 0

(ii) 0

Question. 40

Give possible expressions for the length and breadth of the rectangle whose area is given by \(4a^2 + 4a - 3\).

Answer:

Length = \(2a - 1\), Breadth = \(2a + 3\)

Exercise 2.4: Long Answer Questions

Question. 1

If the polynomials \(az^3 + 4z^2 + 3z - 4\) and \(z^3 - 4z + a\) leave the same remainder when divided by \(z - 3\), find the value of \(a\).

Answer:

\(-1\)

Question. 2

The polynomial \(p(x) = x^4 - 2x^3 + 3x^2 - ax + 3a - 7\) when divided by \(x + 1\) leaves the remainder \(19\). Find the value of \(a\). Also find the remainder when \(p(x)\) is divided by \(x + 2\).

Answer:

\(a = 5\)

Remainder when divided by \(x + 2\) is \(62\).

Question. 3

If both \(x - 2\) and \(x - \dfrac{1}{2}\) are factors of \(px^2 + 5x + r\), show that \(p = r\).

Question. 4

Without actual division, prove that \(2x^4 - 5x^3 + 2x^2 - x + 2\) is divisible by \(x^2 - 3x + 2\).

Hint: Factorise \(x^2 - 3x + 2\).

Question. 5

Simplify \((2x - 5y)^3 - (2x + 5y)^3\).

Answer:

\(-120x^2y - 250y^3\)

Question. 6

Multiply \(x^2 + 4y^2 + z^2 + 2xy + xz - 2yz\) by \((-z + x - 2y)\).

Answer:

\(x^3 - 8y^3 - z^3 - 6xyz\)

Question. 7

If \(a, b, c\) are all non-zero and \(a + b + c = 0\), prove that \(\dfrac{a^2}{bc} + \dfrac{b^2}{ca} + \dfrac{c^2}{ab} = 3\).

Question. 8

If \(a + b + c = 5\) and \(ab + bc + ca = 10\), then prove that \(a^3 + b^3 + c^3 - 3abc = -25\).

Question. 9

Prove that \((a + b + c)^3 - a^3 - b^3 - c^3 = 3(a + b)(b + c)(c + a)\).

NCERT Exemplar Solutions Class 9 – Mathematics – CHAPTER 2: POLYNOMIALS | Detailed Answers