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Published on: 11/10/2019
Polynomials
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1.
If \(\alpha\) and \(\beta\) are zeroes of the polynomial p(x) = 6x2 - 5x + k such that \(\alpha-\beta=\frac{1}{6}\), find the value of k.
2.
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 \(\frac { 1-\beta}{ 1+\beta} \)
3.
Polynomial x4 + 7x3 + 7x2 + px + q is exactly divisible by x2 + 7x + 12, then find the value of p and q.
4.
The graph of y=p(x) is given, where p(x) is a polynomial. Find the number of zeros of p(x).

5.
If polynomial 6x4+8x3+17x2+21x+7 is divided by another polynomial 3x2+4x+1, then what will be the quotient and remainder?
6.
Find other zeroes of the polynomial 2x4-3x3-5x2+9x-3, if it is given that two of its zeroes are \(-\sqrt { 3 } \) and \(\sqrt { 3 } \) , respectively
7.
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).
8.
Obtain all other zeroes of the polynomial x4+7x3+7x2-35x-60, if two of its zeroes are -3 and -4.
9.
If α and β are zeroes of the quadratic polynomial p(x)=6x2+x-1, then find the value of \(\frac { \alpha }{ \beta } +\frac { \alpha }{ \alpha } +2\left( \frac { 1 }{ \alpha } +\frac { 1 }{ \beta } \right) +3\alpha \beta \)
10.
If 1 and -1 are zeroes of polynomial Lx4+Mx3+Nx2+Rx+P, then show that L+N+P=M+R.
11.
Find the quadratic polynomial, whose sum of zeroes is 8 and their products is 12. Then, find the zeroes of the polynomial.
12.
Find the zeroes of quadratic polynomial y2+92y+1920.
13.
Find the degree of the following polynomial
(i) \(7y^{ 5 }+6y^{ 2 }-1\)
(ii) \(\frac { y^{ 4 }+3y^{ 2 }+y }{ y } \)
14.
If α and β are the zeroes of the polynomial 2y2+7y+5, then find the value of α+β+αβ.
15.
If 2 is a zero of polynomial f(x)=ax2-3(a-1)x-1, then find the value of a.
1.
According to the question, \(\alpha\) and \(\beta\) are zeroes of the polynomial p(x) = 6x2 - 5x + k
So, Sum of zeroes = \(\alpha +\beta =-\left( \frac { -5 }{ 6 } \right) =\frac { 5 }{ 6 } \) ... (i)
Product of zeroes = \(\alpha \beta =\frac { k }{ 6 } \)
\(\alpha-\beta=\frac{1}{6}\) (Given) ...... (ii)
Adding equations (i) and (ii), we get
\(2\alpha=2\)
\(\Rightarrow \quad \alpha=\frac{1}{2}\)
Putting the value of \(\alpha\) in equation (ii), we get
\(\frac{1}{2}-\beta=\frac{1}{6}\)
\(\Rightarrow \quad \frac{1}{2}-\frac{1}{6}=\beta\)
\(\Rightarrow \quad \frac{2}{6}=\frac{1}{3}=\beta\)
\(\therefore \quad \alpha\beta=\frac{k}{6}=\frac{1}{2}\times\frac{1}{3}\)
\(\therefore \quad k=1\)
2.
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
3.
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
4.
The graph of y = p(x) does not intersect the X-axis at any point. So, it has no zero.
5.
Quotient=2x2+5, remainder=x+2
6.
\(1,\frac { 1 }{ 2 } \)
7.
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
8.
\(\sqrt { 5 } ,-\sqrt { 5 } \)
9.
\(\frac { \alpha }{ \beta } +\frac { \alpha }{ \alpha } +2\left( \frac { 1 }{ \alpha } +\frac { 1 }{ \beta } \right) +3\alpha \beta \)
\(=\frac { \alpha ^{ 2 }+\beta ^{ 2 } }{ \alpha \beta } +2\left( \frac { \alpha +\beta }{ \alpha \beta } \right) +3\alpha \beta =-\frac { 2 }{ 3 } \)
10.
Let f(x)=Lx4+Mx3+Nx2+Rx+P.
Then, we have f(1)=0
and f(-1)=0
⇒ L+M+N+R+P=0 ..(i)
and L-M+N-R+P=0 ...(ii)
From Eq. (ii), we have L+N+P=M+R
11.
Now, for finding zeroes, put x2-8x+12=0
⇒ (x-6)(x-2)=0⇒ x=2, 6
Hence, the required quadratic polynomial is x2-8x+12 and their zeroes are 2 and 6.
12.
Let p(y)=y2+92y+1920=(y+32)(y+60)
Now, for zeroes of p(y), put p(y)=0
Zeroes y=-32, -60
13.
(i) 5
(ii) 3
14.
α+β+αβ=\(-\frac { 7 }{ 2 } +\frac { 5 }{ 2 } =-1\)
15.
\(f(2)=0\Rightarrow \alpha =\frac { 5 }{ 2 } \)
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