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Published on: 16/08/2019
Polynomials
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1.
If \(\alpha\) and \(\beta\) are the zeroes of the polynomial x2 + 8x + 6 from a quadratic polynomial whose zeroes are \(\frac{1}{\alpha}\) and \(\frac{1}{\beta}\)
2.
If zeroes of the polynomial x2 + 4x + 2a are \(\alpha\) and \(\frac{2}{\alpha}\), then find the value of a.
3.
In the given figure, the graph of a polynomial p(x) is shown. Find the number of zeros of P(x).

4.
Find the zeroes of the given polynomial by factorisation method and verify the relations between the zeroes and the coefficients of the polynomials \(7y^{ 2 }-\frac { 11 }{ 3 } Y-\frac { 2 }{ 3 } \)
5.
If a and β are the zeroes of the quadratic polynomial f(x)=ax2+bx+c, then find the difference between the zeroes.
\(\left( \alpha -\beta \right) ^{ 2 }=\left( \alpha +\beta \right) ^{ 2 }-4\alpha \beta \quad or\quad \left( \alpha -\beta \right) =\pm \sqrt { \left( \alpha +\beta \right) ^{ 2 }-4\alpha \beta } \)
6.
If 2 is a zero of polynomial p(x)=4x2+2x-5a, then find the value of a.
7.
Write the degree of the following polynomials.
\(7q^{ 6 }+4q^{ 2 }+\frac { 3 }{ 2 } +q-8\)
8.
If \(\alpha\) and \(\beta\) are the zeroes of a polynomial \({ x }^{ 2 }-4\sqrt { 3 } x+3\), then find the value of \(\alpha+\beta-\alpha\beta\)
9.
Find the condition that zeroes of polynomial p(x) = ax2 + bx + c are reciprocal of each other.
10.
Find the quadratic polynomial whose sum and product of the zeroes are \(\frac{21}{8}\) and \(\frac{5}{16}\) respectively.
11.
Find all the zeroes of f(x) = x2 - 2x
12.
For a quadratic polynomial, whose one zero is 8 and the product of zeroes is -56.
13.
If one zero of the polynomial (a2+9)x2+13x+6a is a reciprocal of the other, then find the value of a.
14.
Write whether the following expressions are polynomials or nt. Give reasons for your answer.
(i) \(x^{ 3 }+\frac { 1 }{ x^{ 2 } } +\frac { 1 }{ x } +1\)
(ii) x2+x+3
(iii) y-12-3y+2
(iv) \(\sqrt { 2 } y^{ 3 }+\sqrt { 3 } y\)
15.
If the product of the zeroes of the polynomial (ax2-6x-6) is 4, then find the value of a.
16.
Identify the type of the polynomials given below:
\(f(p)=3-p^{ 2 }+\sqrt { 7 } p\)
17.
If \(\alpha\) and \(\beta\) are the zeroes of the polynomial x2 +4x + 3, find the polynomial whose zeroes are \(1+\frac { \beta }{ \alpha } \) and \(1+\frac { \alpha }{ \beta} \)
18.
Polynomial x4 + 7x3 + 7x2 + px + q is exactly divisible by x2 + 7x + 12, then find the value of p and q.
19.
Find all the zeroes of 2x4-3x3-3x2+6x-2, if you know that two of its zeroes are \(\sqrt { 2 } \) and \(-\sqrt { 2 } \) .
20.
If α and β are the zeroes of the quadratic polynomial p(s)=3s2-6s+4, then find the value of \(\frac { a }{ \beta } +\frac { \beta }{ a } +2\left( \frac { 1 }{ a } +\frac { 1 }{ \beta } \right) +3a\beta \) .
21.
Find the value of k, for which polynomial p(x) is exactly divisible by polynomial g(x), in each of the following
(i) p(x)=x3+8x2+kx+18, g(x)=x2+6x+9
(ii) p(x)=x4+10x3+25x2+15x+k, g(x)=x+7
22.
If α and β are zeroes of the quadratic polynomial p(x)=6x2+x-1, then find the value of \(\frac { \alpha }{ \beta } +\frac { \alpha }{ \alpha } +2\left( \frac { 1 }{ \alpha } +\frac { 1 }{ \beta } \right) +3\alpha \beta \)
1.
From the given polynomial we will find the value, the sum of the zeroes, and the multiple of the zeroes.
\(\alpha+\beta=\frac{-b}{a}=\frac{-8}{1}=-8\)
\(\alpha\times\beta=\frac{c}{a}=\frac{6}{1}=6\)
Sum of zeroes = \(\frac { 1 }{ \alpha } +\frac { 1 }{ \beta } =\frac { \alpha +\beta }{ \alpha \beta } =\frac { -8 }{ 6 } =\frac { -4 }{ 3 } \)
Product of zeroes = \(\frac { 1 }{ \alpha } \times \frac { 1 }{ \beta } =\frac { 1 }{ \alpha \beta } =\frac { 1 }{ 6 } \)
Now for making a polynomial
p(x) = x2 - \((\alpha+\beta)x+\alpha\beta\)
\(\therefore\) The polynomial is : \(p(x)=\frac { 1 }{ 6 } \left( 6{ x }^{ 2 }+8x+1 \right) \)
2.
Given, \(\alpha\) and \(\frac{2}{\alpha}\) are the zeroes of x2 + 4x + 2a.
We know that,
Product of the zeroes = \(=\frac { Constant\quad term }{ Coefficient\quad of\quad { x }^{ 2 } } \)
\(\Rightarrow \quad \alpha\times\frac{2}{\alpha}=\frac{2a}{1}\)
\(\Rightarrow 2=2a\)
\(\therefore \quad a=1\)
3.
Here, the graph of p(x) intersects X-axis at one point only
\(\therefore\) Number of zeroes of p(x) = 1
4.
Let \(f(y)=7y^{ 2 }-\frac { 11 }{ 3 } y-\frac { 2 }{ 3 }\)
\(=\frac { 21y^{ 2 }-11y-2 }{ 3 } \)
\(=\frac { 21y^{ 2 }-14y+3y-2 }{ 3 } \) [by splitting the middle term]
\(=\frac { 7y(3y-2)+1(3y-2) }{ 3 } \)
\(=\frac { 1 }{ 3 } (3y-2)(7y+1)\)
So, the value of \(7y^{ 2 }-\frac { 11 }{ 3 } y-\frac { 2 }{ 3 } \) is zero whe 3y-2=0 or 7y+1=0, i.e. when \(y=\frac { 2 }{ 3 } \) or \(y=\frac { 1 }{ 7 } \).
Thus, the zeroes\(=\frac { 2 }{ 3 } -\frac { 1 }{ 7 } =\frac { 14-3 }{ 21 } =\frac { 11 }{ 21 } =-\left( \frac { -11 }{ 3\times 7 } \right) \)
\(=-(1).\left( \frac { Coefficient \ of \ y }{ Coefficient \ of \ y^{ 2 } } \right) \) and product of zeroes\(=\left( \frac { 2 }{ 3 } \right) \left( -\frac { 1 }{ 7 } \right) =\frac { -2 }{ 21 } =\frac { -2 }{ 3\times 7 } \)
\(=\left( \frac { Constant \ term }{ Coefficient \ of \ y^{ 2 } } \right) \)
Hence, the relations between the zeroes and the coefficients of the polynomials is verified.
5.
Given, a and β are the zeroes of f(x)=ax2+bx+c.
\(\alpha +\beta =-\frac { Coefficient \ of \ x }{ Coefficient \ of\ x^{ 2 } } =-\frac { b }{ a } \) ....(i)
and \(\alpha \beta =\frac { Constant \ term }{ Coefficient \ of \ x^{ 2 } } =\frac { c }{ a } \) .....(ii)
We know that,
\(\left( \alpha -\beta \right) ^{ 2 }=\left( \alpha +\beta \right) ^{ 2 }-4\alpha \beta \)
\(\left( \alpha -\beta \right) ^{ 2 }=\left( \frac { -b }{ a } \right) ^{ 2 }-4\left( \frac { c }{ a } \right) \) [from Eqs. (i) and (ii)]
\(=\frac { b^{ 2 } }{ a^{ 2 } } -\frac { 4c }{ a } =\frac { b^{ 2 }-4c }{ a^{ 2 } } \)
On taking square root both sides, we get
\(\alpha -\beta =\pm \frac { 1 }{ a } \sqrt { b^{ 2 }-4c } \)
which is the required difference between their zeroes.
6.
Given polynomial is p(x)=4x2+2x-5a.
Since, 2 is a zero of polynomial.
p(2)=0
⇒ 4(2)2+2(2)-5a=0 [putting x=2]
⇒ 16+4-5a=0 ⇒ 5a=20
\(\therefore\) \(a=\frac { 20 }{ 5 } =4\)
7.
In the polynomial \(7q^{ 6 }+4q^{ 2 }+\frac { 3 }{ 2 } +q-8\) , the highest power of the variable q is 6.
8.
\({ x }^{ 2 }-4\sqrt { 3 } x+3=0\)
If \(\alpha\) and \(\beta\) are the zeroes of \({ x }^{ 2 }-4\sqrt { 3 } x+3\)
then \(\alpha+\beta=-\frac{b}{a}\)
\(\Rightarrow \quad \alpha +\beta =-\frac { \left( -4\sqrt { 3 } \right) }{ 1 } \)
\(\Rightarrow \quad \alpha +\beta=4\sqrt { 3 }\)
and \(\alpha\beta=\frac{c}{a}\)
\(\Rightarrow \quad \alpha\beta=\frac{3}{1}\)
\(\Rightarrow \quad \alpha\beta=3\)
\(\therefore \quad \alpha +\beta -\alpha \beta =4\sqrt { 3 } -3\)
9.
p(x) = ax2 + bx + c
Let \(\alpha\) and \(\frac{1}\alpha\) be the zeroes of p(x), then
Product of zeroes, \(\alpha\times\frac{1}\alpha=\frac{c}{a}\)
So,required condition is, c = a.
10.
According to the question,
Sum of zeroes = \(\frac{21}{8}\)
and Product of zeroes = \(\frac{5}{16}\)
So, quadratic polynomial = x2 - (Sum of zeroes)x + Product of zeroes
= x2 - \(\left( \frac { 21 }{ 8 } \right) \)x + \(\left( \frac { 5 }{ 16 } \right) \)
= \(\frac { 1 }{ 16}\left( 16{ x }^{ 2 }-42x+5 \right) \)
= \(\left( 16{ x }^{ 2 }-42x+5 \right) \frac { 1 }{ 16}\)
11.
f(x) = x2 - 2x
= x(x - 2)
i.e. f(x) = 0 \(\Rightarrow \) x = 0 or x = 2
Hence zeroes are 0 & 2.
12.
x2-x-56
13.
Let α and \(\frac { 1 }{ \alpha } \) be two zeroes of the given polynomial, which are reciprocal of each other.
On comparing the given polynomial with Ax2+Bx+C, we get
A=a2+9, B=13 and C=6a
Now, product of zeroes,
\(\alpha \times \frac { 1 }{ \alpha } =\frac { Constant \ term }{ Coefficient \ of \ x^{ 2 } } \)
\(\\ \Rightarrow \ 1=\frac { 6\alpha }{ a^{ 2 }+9 }\)
\( \\ \Rightarrow \ a^{ 2 }+9=6a\)
\(\\ \Rightarrow \ a^{ 2 }-6a+9=0\)
\(\\ \Rightarrow \ (a-3)^{ 2 }=0\ \ \left[ \because \quad (x-y)^{ 2 }=x^{ 2 }+y^{ 2 }-2xy \right] \)
\(\\ \therefore \ a=3\)
14.
We know that a polynomial in one variable x, is an algebraic expression of the form,
\(p(x)=a_{n} x^{n}+a_{n-1} x^{n-1}+\ldots+a_{1} x+a_{0}\) where n is a positive integer and a0, a1, a2,..., an are constants.
(i) No, because powers of any polynomial is always positive integer.
(ii) Yes, because it satisfies the definition of polynomial.
(iii) No, because powers of any polynomial can not be negative integer.
(iv) Yes, because it satisfies the condition of polynomial.
15.
\(a=-\frac { 3 }{ 2 } \)
16.
Quadratic
17.
Since \(\alpha\) and \(\beta\) are the zeroes of the cubic polynomial x2 +4x + 3
then, \(\alpha+\beta=-4 \)
and \(\alpha\beta=3\)
Sum of zeroes \(=1+\frac { \beta }{ \alpha } +1+\frac { \alpha }{ \beta } \)
\(=\frac { \alpha \beta +{ \beta }^{ 2 }+\alpha \beta +{ \alpha }^{ 2 } }{ \alpha \beta } \)
\(=\frac { { \alpha }^{ 2 }+{ \beta }^{ 2 }+2\alpha \beta }{ \alpha \beta } \)
\(=\frac { \left( \alpha +\beta \right) ^{ 2 } }{ \alpha \beta } =\frac { \left( -4 \right) ^{ 2 } }{ 3 } =\frac { 16 }{ 3 } \)
Product of zeroes = \(\left( 1+\frac { \beta }{ \alpha } \right) \left( 1+\frac { \alpha }{ \beta } \right) \)
\(=1+\frac { \alpha }{ \beta } +\frac { \beta }{ \alpha } +\frac { \alpha \beta }{ \alpha \beta } \)
\(\frac { { \alpha }^{ 2 }+{ \beta }^{ 2 }+2\alpha \beta }{ \alpha \beta } =\frac { \left( \alpha +\beta \right) ^{ 2 } }{ \alpha \beta } \)
\(=\frac { \left( -4 \right) ^{ 2 } }{ 3 } =\frac { 16 }{ 3 } \)
But required polynomial = x2 - (Sum of the zeroes) x + Product of the zeroes
\(={ x }^{ 2 }-\left( \frac { 16 }{ 3 } \right) x+\frac { 16 }{ 3 } \)
or \(=\left( { x }^{ 2 }-\frac { 16 }{ 3 } x+\frac { 16 }{ 3 } \right) \)
\(=\left( 3{ x }^{ 2 }-16x+16 \right) \frac { 1 }{ 3 } \)
18.
Factors of x2 + 7x + 12 :
x2 + 7x + 12 = 0
\(\Rightarrow\) x2 + 4x + 3x + 12 = 0
\(\Rightarrow\) x(x + 4) + 3 (x + 4) = 0
\(\Rightarrow\) (x + 4) (x + 3) = 0
\(\Rightarrow\) x = - 4, - 3 .... (i)
Let p'(x) = x4 + 7x3 + 7x2 + px + q
If p(x) is exactly divisible by x2 + 7x + 12, then x = - 4 and x = - 3 are zeroes of p(x) [from eq (i)]
p(x) = x4 + 7x3 + 7x2 + px + q
p(- 4) = (-4)4 + 7(-4)3 + 7(-4)2 + p(-4) + q
but p(-4) = 0
\(\therefore\) 0 = 256 - 448 + 112 - 4p + q
\(\Rightarrow\) 0 = - 4p + q - 80
\(\Rightarrow\) 4p - q = 80 ... (ii)
and p(-3) = (-3)4 + 7 (-3)3 + 7(-3)2 + p(-3) + q
but p(-3) = 0
\(\therefore\) 0 = 81 - 189 + 63 - 3p + q
\(\Rightarrow\) 0 = -3 p+ q - 45
\(\Rightarrow\) 3p - q = - 45
On solving eq.(ii) and eq. (iii) by elimination method, we get
4p - q = - 80
3p - q = - 45
p = - 35
On putting the value of p in eq. (i),
4(- 35) - q = - 80
\(\Rightarrow\) - 140 - q = - 80
\(\Rightarrow\) - q = 140 - 80
\(\Rightarrow\) - q = 60
\(\Rightarrow\) q = - 60
Hence, p = - 35, q = - 60
19.
Let p(x)=2x4-3x3-3x2+6x-2.
Since, its two zeroes are \(\sqrt { 2 } \) and \(-\sqrt { 2 } \).
So, (x-\(\sqrt { 2 } \)) and (x+\(-\sqrt { 2 } \)) are the factors of p(x).
⇒ (x-\(\sqrt { 2 } \)) (x+\(-\sqrt { 2 } \)) is a factor of p(x).
⇒ x2-2 also a factor of p(x).
Now, let us divide the given polynomial p(x) by g(x)=x2-2. Then division process is
Here, quotient=2x2-3x+1 and remainder=0
Now, factorise the quotient by splitting the middle term, i.e. write
2x2-3x+1=2x2-2x-x+1
=2x(x-1)-1(x-1)=(2x-1)(x-1)
So, other zeroes of f(x) are given by
(2x-1)=0 and (x-1)=0
⇒ \(x=\frac { 1 }{ 2 } \) and x=1
Hence, all the zeroes of 2x4-3x3-3x2+6x-2 are \(\sqrt { 2 } \), \(-\sqrt { 2 } \), \(\frac{1}{2}\) and 1.
20.
Given, α and β are the zeroes of the quadratic polynomial p(s)=3s2-6s+4.
\(\therefore \ a+\beta =-\frac { Coefficient \ of \ s }{ Coefficient \ of \ s^{ 2 } } =\frac { -(-6) }{ 3 } =\frac { 6 }{ 3 } =2\)
and \(a\beta =\frac { Constant \ term }{ Coefficient \ of \ s^{ 2 } } =\frac { 4 }{ 3 } \)
Now, \(\frac { a }{ \beta } +\frac { \beta }{ a } +2\left( \frac { 1 }{ a } +\frac { 1 }{ \beta } \right) +3a\beta \)
\(=\frac { a^{ 2 }+\beta ^{ 2 } }{ a\beta } +2\left( \frac { a+\beta }{ a\beta } \right) +3a\beta \)
\(=\frac { (a+\beta )^{ 2 } }{ a\beta } +2\left( \frac { a+\beta }{ a\beta } \right) +3a\beta \)
\(\left[ \because \quad a^{ 2 }+b^{ 2 }=(a+b)^{ 2 }-2ab \right] \)
\(=\frac { (2)^{ 2 }-2(4/3) }{ 4/3 } +2\left( \frac { 2 }{ 4/3 } \right) +3\times \frac { 4 }{ 3 } \)
\(\quad \left[ \because \quad a+\beta =2\quad and\quad a\beta =4/3 \right] \)
\(=\frac { 4-\frac { 8 }{ 3 } }{ \frac { 4 }{ 3 } } +2\times 2\times \frac { 3 }{ 4 } +3+4\)
\(=\frac { 4 }{ 3 } \times \frac { 3 }{ 4 } +7=1+7=8\)
21.
(i) On dividing p(x) by g(x), we get
Quotient, q(x)=x+2 and remainder, r(x)=(k-21)x
Since, p(x) is exactly divisible by g(x), so remainder =0
⇒ (k-21) x=0⇒ (k-21) x=0.x
On comparing coefficient of x, we get
k-21=0⇒k=21
22.
\(\frac { \alpha }{ \beta } +\frac { \alpha }{ \alpha } +2\left( \frac { 1 }{ \alpha } +\frac { 1 }{ \beta } \right) +3\alpha \beta \)
\(=\frac { \alpha ^{ 2 }+\beta ^{ 2 } }{ \alpha \beta } +2\left( \frac { \alpha +\beta }{ \alpha \beta } \right) +3\alpha \beta =-\frac { 2 }{ 3 } \)
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