NCERT Exemplar Solutions
Class 10 - Mathematics
CHAPTER 2: Polynomials

Zeroes, relations with coefficients, division algorithm.

Exercise 2.1

Choose the correct answer (MCQs).

Question.  1

If one of the zeroes of the quadratic polynomial \((k-1)x^2 + kx + 1\) is \(-3\), then the value of k is

(A)

\(\dfrac{4}{3}\)

(B)

\(-\dfrac{4}{3}\)

(C)

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

(D)

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

Open

Question.  2

A quadratic polynomial, whose zeroes are \(-3\) and \(4\), is

(A)

\(x^2 - x + 12\)

(B)

\(x^2 + x + 12\)

(C)

\(\dfrac{x^2}{2} - \dfrac{x}{2} - 6\)

(D)

\(2x^2 + 2x - 24\)

Open

Question.  3

If the zeroes of the quadratic polynomial \(x^2 + (a+1)x + b\) are \(2\) and \(-3\), then

(A)

\(a = -7,\; b = -1\)

(B)

\(a = 5,\; b = -1\)

(C)

\(a = 2,\; b = -6\)

(D)

\(a = 0,\; b = -6\)

Open

Question.  4

The number of polynomials having zeroes as \(-2\) and \(5\) is

(A)

1

(B)

2

(C)

3

(D)

more than 3

Open

Question.  5

Given that one of the zeroes of the cubic polynomial \(ax^3+bx^2+cx+d\) is zero, the product of the other two zeroes is

(A)

\(-\dfrac{c}{a}\)

(B)

\(\dfrac{c}{a}\)

(C)

0

(D)

\(-\dfrac{b}{a}\)

Open

Question.  6

If one of the zeroes of the cubic polynomial \(x^3+ax^2+bx+c\) is \(-1\), then the product of the other two zeroes is

(A)

\(b-a+1\)

(B)

\(b-a-1\)

(C)

\(a-b+1\)

(D)

\(a-b-1\)

Open

Question.  7

The zeroes of the quadratic polynomial \(x^2 + 99x + 127\) are

(A)

both positive

(B)

both negative

(C)

one positive and one negative

(D)

both equal

Open

Question.  8

The zeroes of the quadratic polynomial \(x^2 + kx + k\), where \(k \ne 0\), are:

(A)

cannot both be positive

(B)

cannot both be negative

(C)

are always unequal

(D)

are always equal

Open

Question.  9

If the zeroes of the quadratic polynomial \(ax^2 + bx + c\), with \(c \ne 0\), are equal, then

(A)

\(c\) and \(a\) have opposite signs

(B)

\(c\) and \(b\) have opposite signs

(C)

\(c\) and \(a\) have the same sign

(D)

\(c\) and \(b\) have the same sign

Open

Question.  10

If one of the zeroes of a quadratic polynomial of the form \(x^2+ax+b\) is the negative of the other, then it

(A)

has no linear term and the constant term is negative

(B)

has no linear term and the constant term is positive

(C)

can have a linear term but the constant term is negative

(D)

can have a linear term but the constant term is positive

Open

Question.  11

Which of the following is not the graph of a quadratic polynomial?

(A)

(B)

(C)

(D)

Open

Exercise 2.2

Short answer questions with reasoning.

Question. 1

Answer the following and justify:
(i) Can \(x^2-1\) be the quotient on division of \(x^6+2x^3+x-1\) by a polynomial in \(x\) of degree 5?
(ii) What will the quotient and remainder be on division of \(ax^2+bx+c\) by \(px^3+qx^2+rx+s\), \(p\ne0\)?
(iii) If on division of a polynomial \(p(x)\) by a polynomial \(g(x)\), the quotient is zero, what is the relation between \(\deg p\) and \(\deg g\)?
(iv) If on division of a non-zero polynomial \(p(x)\) by a polynomial \(g(x)\), the remainder is zero, what is the relation between \(\deg p\) and \(\deg g\)?
(v) Can the quadratic polynomial \(x^2+kx+k\) have equal zeroes for some odd integer \(k>1\)?

Answer:

(i) No   (ii) Quotient 0, remainder \(ax^2+bx+c\)   (iii) \(\deg p<\deg g\)   (iv) \(\deg p\ge \deg g\)   (v) No

Open

Question. 2

Are the following statements True/False? Justify:
(i) If the zeroes of a quadratic polynomial \(ax^2+bx+c\) are both positive, then \(a,b,c\) all have the same sign.
(ii) If the graph of a polynomial intersects the x-axis at only one point, it cannot be a quadratic polynomial.
(iii) If the graph of a polynomial intersects the x-axis at exactly two points, it need not be a quadratic polynomial.
(iv) If two of the zeroes of a cubic polynomial are zero, then it does not have linear and constant terms.
(v) If all the zeroes of a cubic polynomial are negative, then all the coefficients and the constant term have the same sign.
(vi) If all three zeroes of a cubic polynomial \(x^3+ax^2-bx+c\) are positive, then at least one of \(a,b,c\) is non-negative.
(vii) The only value of \(k\) for which the quadratic polynomial \(kx^2+x+k\) has equal zeroes is \(\dfrac{1}{2}\).

Answer:

(i) False   (ii) False   (iii) True   (iv) True   (v) True   (vi) False   (vii) False

Open

Exercise 2.3

Find the zeroes of the following polynomials by factorisation method and verify the relations between the zeroes and the coefficients of the polynomials:

Question. 1

Find the zeroes of \(4x^2-3x-1\) by factorisation and verify relations.

Answer:

\(x=1,\; x=-\dfrac{1}{4}\)

Open

Question. 2

Find the zeroes of \(3x^2+4x-4\) and verify relations.

Answer:

\(x=\dfrac{2}{3},\; x=-2\)

Open

Question. 3

Find the zeroes of \(5t^2+12t+7\) and verify relations.

Answer:

\(t=-1,\; t=-\dfrac{7}{5}\)

Open

Question. 4

Find the zeroes of \(t^3-2t^2-15t\) and verify relations.

Answer:

\(t=0,\; t=5,\; t=-3\)

Open

Question. 5

Find the zeroes of \(2x^2+\dfrac{7}{2}x+\dfrac{3}{4}\) and verify relations.

Answer:

\(x=-\dfrac{1}{4},\; x=-\dfrac{3}{2}\)

Open

Question. 6

Find the zeroes of \(4x^2+5\sqrt{2}x-3\) and verify relations.

Answer:

\(x=\dfrac{\sqrt{2}}{4},\; x=-\dfrac{3\sqrt{2}}{2}\)

Open

Question. 7

Find the zeroes of \(2s^2-(1+2\sqrt{2})s+\sqrt{2}\) and verify relations.

Answer:

\(s=\dfrac{1}{2},\; s=\sqrt{2}\)

Open

Question. 8

Find the zeroes of \(v^2+4\sqrt{3}v-15\) and verify relations.

Answer:

\(v=\sqrt{3},\; v=-5\sqrt{3}\)

Open

Question. 9

Find the zeroes of \(y^2+\dfrac{\sqrt{3}}{2}y-5\) and verify relations.

Answer:

\(y=\dfrac{-\sqrt{3}+\sqrt{83}}{4},\; y=\dfrac{-\sqrt{3}-\sqrt{83}}{4}\)

Open

Question. 10

Find the zeroes of \(7y^2-\dfrac{11}{3}y-23\) and verify relations.

Answer:

\(y=\dfrac{11+\sqrt{5917}}{42},\; y=\dfrac{11-\sqrt{5917}}{42}\)

Open

Exercise 2.4

Construct polynomials and find zeroes.

Question. 1i

For each of the following, find a quadratic polynomial whose sum and product respectively of the zeroes are as given. Also find the zeroes of these polynomials by factorisation.

(i). \(-\dfrac{8}{3}\), \(\dfrac{4}{3}\)

(ii). \(\dfrac{21}{8}\), \(\dfrac{5}{16}\)

(iii). \(-2\sqrt{3}\), \(-9\)

(iv). \(-\dfrac{3}{2\sqrt{5}}\), \(-\dfrac{1}{2}\)

Answer:

(i) Polynomial: \(3x^2 + 8x + 4\); Zeroes: \(x=-2\), \(x=-\dfrac{2}{3}\).

(ii) Polynomial: \(16x^2 - 42x + 5\); Zeroes: \(x=\dfrac{5}{2}\), \(x=\dfrac{1}{8}\).

(iii) Polynomial: \(x^2 + 2\sqrt{3}x - 9\); Zeroes: \(x=\sqrt{3}\), \(x=-3\sqrt{3}\).

(iv) Polynomial: \(2\sqrt{5}x^2 + 3x - \sqrt{5}\); Zeroes: \(x=\dfrac{1}{\sqrt{5}}\), \(x=-\dfrac{\sqrt{5}}{2}\).

Open

Question. 2

Given that the zeroes of \(x^3-6x^2+3x+10\) are of the form \(a,\, a+b,\, a+2b\), find \(a\), \(b\) and the zeroes.

Answer:

\(a=5,\; b=-3\) (equivalently \(a=-1,\; b=3\)); Zeroes: \(\{5,\,2,\,-1\}\).

Open

Question. 3

Given that \(\sqrt{2}\) is a zero of \(6x^3 + \sqrt{2}x^2 - 10x - 4\sqrt{2}\), find the other two zeroes.

Answer:

Other zeroes: \(x = -\dfrac{\sqrt{2}}{2}\), \(x = -\dfrac{2\sqrt{2}}{3}\).

Open

Question. 4

Find \(k\) so that \(x^2 + 2x + k\) is a factor of \(2x^4 + x^3 - 14x^2 + 5x + 6\). Also find all zeroes of the two polynomials.

Answer:

\(k = -3\).

Zeroes of \(x^2 + 2x - 3\): \(x = 1\), \(x = -3\).

Zeroes of \(2x^4 + x^3 - 14x^2 + 5x + 6\): \(x = -\dfrac{1}{2}\), \(x = 2\), \(x = 1\), \(x = -3\).

Open

Question. 5

Given that \(x - 5\) is a factor of \(x^3 - 3\sqrt{2}\,x^2 + 13x - 3\sqrt{5}\), find all zeroes.

Answer:

\(x = 5\), \(x = \sqrt{2} + \sqrt{5}\), \(x = \sqrt{2} - \sqrt{5}\).

Open

Question. 6

For which values of \(a\) and \(b\), are the zeroes of \(q(x)=x^3+2x^2+a\) also the zeroes of \(p(x)=x^5-x^4-4x^3+3x^2+3x+b\)? Which zeroes of \(p(x)\) are not zeroes of \(q(x)\)?

Answer:

\(a = -1\), \(b = -2\).

Then \(q(x) = x^3 + 2x^2 - 1 = (x + 1)(x^2 + x - 1)\).

And \(p(x) = q(x)\,(x^2 - 3x + 2) = q(x)(x - 1)(x - 2)\).

So, the zeroes common to both are the three zeroes of \(q\): \(x = -1\), \(x = \dfrac{-1 \pm \sqrt{5}}{2}\).

The zeroes of \(p\) that are not zeroes of \(q\) are \(x = 1\) and \(x = 2\).

Open

NCERT Exemplar Solutions Class 10 – Mathematics – CHAPTER 2: Polynomials | Detailed Answers