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Published on: 01/08/2018
In this question paper, some of the important questions are covered in the chapter Polynomials. The questions are prepared from the book back and previous year questions.
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1.
If \(\alpha\) and \(\beta\) are the zeroes of a quadratic polynomial such that \(\alpha+\beta=24\) and \(\alpha-\beta=8\). Find the quadratic polynomial having \(\alpha\) and \(\beta\) as its zeroes. Verify the relationship between the zeroes and coefficients of the polynomial.
2.
Find the zeroes of the quadratic polynomial 5x2 + 8x - 4 and verify the relationship between the zeroes and the coefficients of the polynomial.
3.
Show that \(\frac{1}{2}\) and \(\frac{-3}{2}\) are the zeroes of the polynomial 4x2 + 4x - 3 and verify the relationship between zeroes and coefficients of the polynomial.
4.
Quadratic polynomial 2x2 - 3x + 1 has zeroes as \(\alpha\) and \(\beta\). Now form a quadratic polynomial whose zeroes are \(3\alpha\) and \(3\beta\).
5.
Verify whether 2, 3 and \(\frac{1}{2}\) are the zeroes of the polynomial p(x) = 2x3 - 11x2 + 17x - 6.
6.
If α and β are zeroes of a quadratic polynomial x2 -5, then form a quadratic polynomial whose zeroes are 1+α and 1+β.
7.
If a and β are the zeroes of the quadratic polynomial f(x)=ax2+bx+c, then find the difference between the zeroes.
\(\left( \alpha -\beta \right) ^{ 2 }=\left( \alpha +\beta \right) ^{ 2 }-4\alpha \beta \quad or\quad \left( \alpha -\beta \right) =\pm \sqrt { \left( \alpha +\beta \right) ^{ 2 }-4\alpha \beta } \)
8.
If a and β are zeroes of the polynomial x2-P(x+1)+c such that (a+1) (β+1)=0, then find the value of c.
9.
If \(\alpha\) and \(\beta\) are the zeroes of polynomial p(x) = 3x2 + 2x + 1, find the polynomial whose zeroes are \(\frac { 1-\alpha }{ 1+\alpha } \) and \(\frac { 1-\beta}{ 1+\beta} \)
10.
Polynomial x4 + 7x3 + 7x2 + px + q is exactly divisible by x2 + 7x + 12, then find the value of p and q.
11.
If two zeroes of the polynomial
x4-6x3-26x2+138x-35 are \(2\pm \sqrt { 3 } \), then find other zeroes.
12.
Find all the zeroes of 2x4-3x3-3x2+6x-2, if you know that two of its zeroes are \(\sqrt { 2 } \) and \(-\sqrt { 2 } \) .
13.
A polynomial g(x) of degree zero is added to the polynomial 2x3+5x2-14x+10, so that it becomes exactly divisible by 2x-3. Find g(x).
14.
Find the value for k for which x4 + 10x3 + 25x2 + 15x + k is exactly divisible by x + 7.
15.
Find the values of a and b, if they are the zeroes of polynomial x2 + ax + b.
16.
If \(\alpha\) and \(\beta\) are the zeroes of a polynomial \({ x }^{ 2 }-4\sqrt { 3 } x+3\), then find the value of \(\alpha+\beta-\alpha\beta\)
17.
If m and n are the zeroes of the polynomial 3x2 + 11x - 4, find the value of \(\frac{m}{n}+\frac{n}{m}\)
18.
If zeroes of the polynomial x2 + 4x + 2a are \(\alpha\) and \(\frac{2}{\alpha}\), then find the value of a.
19.
If - 1 is a zero of the polynomial f(x) = x2 - 7x - 8, then calculate the other zero.
20.
If sum of the zeroes of the quadatic polynomial 3x2 - kx + 6 is 3, then find the value of k.
21.
If \(\alpha\) and \(\beta\) are the roots of ax2 - bx + c = 0 \(\left( a\neq 0 \right) \), then calculate \(\alpha+\beta\).
22.
If m and n are the zeroes of the polynomial 3x2+11x-4, then find the value of \(\frac { m }{ n } +\frac { n }{ m } \) .
23.
If α and β are zeroes of the quadratic polynomial p(x)=x2-(k+6)x+2(2k-1), then find the value of k, if \(a+\beta =\frac { a\beta }{ 2 } \) .
1.
Given, \(\alpha+\beta=24\) ... (i)
\(\alpha-\beta=8\) ... (ii)
Adding equations (i) and (ii),
\(2\alpha=32\)
\(\Rightarrow \quad \alpha=16\)
Put the value of \(\alpha\) in equation (i),
\(16+\beta=24\)
\(\Rightarrow \quad \beta=24-16 =8\)
Hence, the quadratic polynomial = x2 - (Sum of zeroes)x + (Product of zeroes)
\(={ x }^{ 2 }-\left( \alpha +\beta \right) x+\alpha \beta \)
\(={ x }^{ 2 }-\left( 16+8 \right) x+(16)(8)\)
\(={ x }^{ 2 }-24 x+128\)
Verification : \(\alpha+\beta=\frac{-b}{a}=-\frac { Coeff. \ of \ x }{ Coeff. \ of \ { x }^{ 2 } } \)
\(\Rightarrow \quad 24=-\left( -\frac { 24 }{ 1 } \right) \)
and \(\alpha \beta =\frac { c }{ a } =\frac { Costant \ term }{ Coeff. \ of \ { x }^{ 2 } } \)
\(\Rightarrow \quad 128=\left( \frac { 128 }{ 1 } \right) \)
Hence, the relationship is verified.
2.
Let p(x) = 5x2 + 8x - 4
= 5x2 + 10x - 2x - 4
= 5x (x + 2) - 2 (x + 2)
= (x + 2) (5x - 2)
Hence, zeroes of the quadratic polynomial 5x2 + 8x - 4 are - 2 and \(\frac{2}{5}\)
Verification :
Sum of zeroes = \(-2+\frac{2}{5}=\frac{-8}{5}\)
Product of zeroes = \((-2)\times(\frac{2}{5})=\frac{-4}{5}\)
Again sum of zeroes \(=-\frac { Coeff. \ of \ x }{ Coeff. \ of \ { x }^{ 2 } } =\frac { -8 }{ 5 } \)
Product of zeroes = \(=\frac { Costant \ term }{ Coeff. \ of \ { x }^{ 2 } } =\frac { -4 }{ 5 } \)
Thus relationship is verified.
3.
f(x) = 4x2 + 4x - 3
\(\Rightarrow \quad f\left( \frac { 1 }{ 2 } \right) =4\left( \frac { 1 }{ 4 } \right) +4\left( \frac { 1 }{ 2 } \right) -3\)
= 1 + 2 - 3 = 0
and \(f\left( \frac { -3 }{ 2 } \right) =4\left( \frac { 9 }{ 4 } \right) +4\left( -\frac { 3 }{ 2 } \right) -3\)
= 9 - 6 - 3 = 0
\(\therefore \quad \frac{1}{2},-\frac{3}{2}\) are zeroes of polynomial 4x2 + 4x - 3
Sum of zeroes = \(\frac{1}{2}-\frac{3}{2}=-1=\frac{-4}{4}\)
\(=-\frac { Coefficient \ of \ x }{ Coefficient \ of \ { x }^{ 2 } } \)
Product of zeroes = \(\left( \frac { 1 }{ 2 } \right) \left( -\frac { 3 }{ 2 } \right) =\frac { -3 }{ 4 } \)
\(=\frac { Costant \ term }{ Coefficient \ of \ { x }^{ 2 } } \)
\(\therefore\) Relation between zeroes and coeff.of polynomial is verified.
4.
If \(\alpha\) and \(\beta\) are the zeroes of 2x2 - 3x + 1,
then \(\alpha+\beta=-\frac{b}{a}\)
\(\Rightarrow \quad \alpha+\beta=\frac{3}{2}\)
and \(\alpha\beta=\frac{c}{a}\)
\(\Rightarrow \quad \alpha\beta=\frac{1}{2}\)
New quadratic polynomial whose zeroes are \(3\alpha\) and \(3\beta\) is :
x2 - (Sum of the roots)x + Product of the roots
= x2 - \((3\alpha+3\beta)x+3\alpha\times3\beta\)
= x2 - 3(\(\alpha+\beta\))x + 9\(\alpha\beta\)
\(={ x }^{ 2 }-3\left( \frac { 3 }{ 2 } \right) x+9\left( \frac { 1 }{ 2 } \right) \)
\(={ x }^{ 2 }-\frac { 9 }{ 2 } x+\frac { 9 }{ 2 } \)
\(=\frac { 1 }{ 2 } \left( 2{ x }^{ 2 }-9x+9 \right) \)
Hence, required quadratic polynomial is \(\frac { 1 }{ 2 } \left( 2{ x }^{ 2 }-9x+9 \right) \)
5.
(i) Now p(x) = 2x3 - 11x2 + 17x - 6
p(2) = 2(2)3 - 11(2)2 + 17(2) - 6
= 16 - 44 + 34 - 6
= 50 - 50
= 0
Hence 2 is the zero of p(x)
(ii) Again p(3) = 2(3)3 - 11(3)2 + 17(3) - 6
= 54 - 99 + 51 - 6
= 105 - 105 = 0
Hence, 3 is zero of p(x)
(iii) Again \(p\left( \frac { 1 }{ 2 } \right) =2\left( \frac { 1 }{ 2 } \right) ^{ 3 }-11\left( \frac { 1 }{ 2 } \right) ^{ 2 }+17\left( \frac { 1 }{ 2 } \right) -6\)
\(=\frac { 1 }{ 4 } -\frac { 11 }{ 4 } +\frac { 17 }{ 2 } -6\)
= 0
Hence, \(\frac{1}{2}\) is also the zero of p(x).
6.
Let P(x)=x2-5
For finding a zeroes of p(x), p(x)=0
x2-5=0
⇒ x=±5
Let α=5 and β=-5
Now, 1+a=1+5=6
and 1-a=1-5=4
Thus, 6 and -4 are the zeroes of new quadratic polynomial.
Therefore the new quadratic polynomial will be (x-6)(x+4) or x2-2x-24
7.
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.
8.
Since, a and β are the zeroes of polynomial x2 -px-p+c.
So, sum of zeroes, a+β =p ...(i)
and product of zeroes, aβ =c-p| ...(ii)
Also, (a+1)(β+1)=0 [given]
aβ+(a+β)+1=0
⇒ c-p+p+1=0 [from Eqs. (i) and (ii)]
⇒ c-1
9.
Since \(\alpha\) and \(\beta\) are the zeroes of polynomial p(x) = 3x2 + 2x + 1
Hence, \(\alpha+\beta=-\frac{2}{3}\)
and \(\alpha\beta=\frac{1}{3}\)
Now for the new polynomial,
Sum of the zeroes = \(\frac { 1-\alpha }{ 1+\alpha } +\frac { 1-\beta}{ 1+\beta} \)
\(=\frac { \left( 1-\alpha +\beta -\alpha \beta \right) +\left( 1+\alpha -\beta -\alpha \beta \right) }{ \left( 1+\alpha \right) \left( 1+\beta \right) } \)
\(=\frac { 2-2\alpha \beta }{ \left( 1+\alpha +\beta +\alpha \beta \right) } =\frac { 2-\frac { 2 }{ 3 } }{ 1-\frac { 2 }{ 3 } +\frac { 1 }{ 3 } } \)
\(\therefore\) Sum of zeroes \(=\frac { { 4 }/{ 3 } }{ { 2 }/{ 3 } } =2\)
Product of zeroes \(=\left[ \frac { 1-\alpha }{ 1+\alpha } \right] \left[ \frac { 1-\beta }{ 1+\beta } \right] \)
\(=\frac { \left( 1-\alpha \right) \left( 1-\beta \right) }{ \left( 1+\alpha \right) \left( 1+\beta \right) } \)
\(=\frac { 1-\alpha -\beta +\alpha \beta }{ 1+\alpha +\beta +\alpha \beta } =\frac { 1-\left( \alpha +\beta \right) +\alpha \beta }{ 1+\left( \alpha +\beta \right) +\alpha \beta } \)
\(\therefore\) Product of zeroes \(=\frac { 1+\frac { 2 }{ 3 } +\frac { 1 }{ 3 } }{ 1-\frac { 2 }{ 3 } +\frac { 1 }{ 3 } } =\frac { \frac { 6 }{ 3 } }{ \frac { 2 }{ 3 } } =3\)
Hence, Required polynomial = x2 - (Sum of zeroes)x + Product of zeroes
= x2 - 2x + 3
10.
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
11.
Let given polynomial be
p(x)=x4 -6x3-26x2+138x-35
Give, \(2\pm \sqrt { 3 } \) are two zeroes of the polynomial.
So, \((x-(2+\sqrt { 3 }) )\) and \((x-(2-\sqrt { 3 }) )\) are factors of p(x)
⇒ \((x-(2+\sqrt { 3 }) )\) \((x-(2-\sqrt { 3 }) )\) is a factor of (p(x)
\(\Rightarrow \quad ((x-2)-\sqrt { 3 } )((x-2)+\sqrt { 3 } )\) is a factor p(x)
\(\Rightarrow \quad (x-2)^{ 2 }-(\sqrt { 3 } )^{ 2 }\) is a factor p(x)
⇒ x2-4x+1 is a factor p(x)
Now, divide p(x) by x2-4x+1 to obtain other zeroes.
Then, the division process is
∴ p(x)=x4 -6x3-26x2+138x-35
-(x2-4x+1)(x2-4x+1)(x2-2x-35)
Now, for other zeores put x2-2x-35=0
⇒ x2-7x+5x-35=0 [ by splitting the middle term]
⇒ [x(x-7)+5(x-7)]=0
⇒ (x+5)(x-7)=0⇒x=5, 7
Hence, -5 and 7 are other zeores of the given polynomial.
12.
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.
13.
Let g(x)=k, then 2x 3 +5x 2 -14x+10+k will be exactly by 2x-3.
On dividing 2x 3 +5x 2 -14x+10+k by 2x-3, we get Quotient x2+4x-1 and remainder 7+k.
Since, 2x 3 +5x 2 -14x+10+k is exactly divisible by 2x-3, so remainder=0
⇒ 7+k=0⇒k=-7
14.
If x + 7 is a factor then (-7) is a root.
So, f(-7) = (-7)4 + 10(-7)3 + 25(-7)2 + 15(-7) + k = 0
(when it is a root the polynomial should be equal to zero when value is substituted)
2401 - 3430 + 1225 - 105 + k = 0
\(\Rightarrow\) 3626 - 3535 + k = 0
\(\Rightarrow\) 91 + k = 0
\(\therefore\) k = - 91
15.
Sum of zeroes \(=-\frac { Coefficient\ of \ x }{ Coefficient \ of \ { x }^{ 2 } } \)
\(\therefore \quad a + b = - a\)
\(\Rightarrow \quad 2a + b = 0\)
Product of zeroes = \(=-\frac { Constant \ term }{ Coefficient \ of \ { x }^{ 2 } } \)
\(\therefore \quad ab = b\)
\(\Rightarrow \quad a=1\)
then b = - 2
16.
\({ x }^{ 2 }-4\sqrt { 3 } x+3=0\)
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 \(\alpha\beta=\frac{c}{a}\)
\(\Rightarrow \quad \alpha\beta=\frac{3}{1}\)
\(\Rightarrow \quad \alpha\beta=3\)
\(\therefore \quad \alpha +\beta -\alpha \beta =4\sqrt { 3 } -3\)
17.
Let p(x) = 3x2 + 11x - 4
= 3x2 + 12x - x - 4
= 3x(x + 4) - 1(x + 4)
= (3x - 1)(x + 4)
So, zeroes are \(m=\frac{1}{3}\) and n = - 4
Now, \(\frac { m }{ n } +\frac { n }{ m } =\frac { \left( \frac { 1 }{ 3 } \right) }{ -4 } +\frac { -4 }{ \left( \frac { 1 }{ 3 } \right) } =\frac { 1 }{ -12 } -12\)
\(=\frac{-145}{12}\)
18.
Comparing x2+4x+2a with ax2+bx+c,
a=1,b=4,c=2a
According to the question,
\(\alpha, \frac{\alpha}{2}\) are the zeroes of the polynomial,
sum of the zeroes \(\frac{\mathrm{b}}{\mathrm{a}}\)
\(\alpha+\frac{\alpha}{2}=\frac{-4}{1}\)
\(\alpha=\frac{-8}{3}\)
\(\alpha^{2}=\frac{64}{9}\) [squaring both sides]
product of all zeroes,
\(\alpha \times \frac{\alpha}{2}=\frac{2 a}{1}\)
α2=4a
\(\therefore 4 \mathrm{a}=\frac{64}{9}\left[\because \alpha^{2}=\frac{64}{9}\right]\)
\(a=\frac{16}{9}\)
19.
f(x) = x2 - 7x - 8
Let other zero be k, then
Sum of zeroes \(-1+k=-\left( \frac { -7 }{ 1 } \right) =7\)
\(\Rightarrow k = 8\)
20.
p(x) = 3x2 - kx + 6
Sum of the zeroes = 3 \(=-\frac { Coefficient\quad of\quad x }{ Coefficient\quad of\quad { x }^{ 2 } } \)
\(\Rightarrow \quad 3=-\frac { \left( -k \right) }{ 3 } \)
k = 9
21.
Sum of the roots \(=-\frac { Coefficient\quad of\quad x }{ Coefficient\quad of\quad { x }^{ 2 } } \)
\(\Rightarrow \quad \alpha +\beta =-\left( \frac { b }{ a } \right) \)
\(=\frac{b}{a}\)
22.
\(-\frac { 145 }{ 12 } \)
23.
k=7
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