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Page No 123:
Question 1:
Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer:
(i) 3x2 − 4x + 15
(ii) y2 + 2
(iii)
(iv)
(v) x12 + y3 + t50
(vi)
(vii)
(viii)
(ix)
Answer:
(i) 3x2 − 4x + 15 is a polynomial of degree 2.i.e Quadratic polynomial.
(ii) y2 + 2 is a polynomial of degree 2 in y variable. i.e. Quadratic polynomial.
(iii)
It is not a polynomial because exponent of x is which is not a positive integer.
(iv)
It is not a polynomial because is fractional part.
(v) x12 + y3 + t50
It is a polynomial in three variables x, y and t.
(vi)
Not polynomial, because the exponent of the variable of is which is not a positive integer.
(vii)
Not polynomial, is a rational expression .
(viii)
Not polynomial, because the exponent of is –1, which is not a whole number.
(ix) is a polynomial of degree 2.i.e Quadratic polynomial.
Page No 123:
Question 2:
Write the coefficient of x2 in each of the following:
(i) 17 − 2x + 7x2
(ii) 9 − 12x + x3
(iii)
(iv)
Answer:
(i)
Coefficient of
(ii)
Coefficient of
(iii)
Coefficient of
(iv)
Coefficient of
Page No 124:
Question 3:
Write the degrees of each of the following polynomials:
(i) 7x3 + 4x2 − 3x + 12
(ii) 12 − x + 2x3
(iii)
(iv) 7
(v) 0
(vi) y3(1 – y4)
Answer:
(i) 7x3 + 4x2 − 3x + 12
Degree of the polynomial = 3
Because the highest power of x is 3.
(ii) 12 − x + 2x3
Degree of the polynomial = 3. Because the highest power of x is 3.
(iii)
Degree of the polynomial = 1. Because the highest power of y is 1.
(iv) 7
Degree of the polynomial = 0. Because there is no variable term in the expression
(v) 0
Degree of the polynomial is not defined. As there is no variable or constant term
(vi) y3(1 – y4)
y3(1 – y4) = y3 – y7, degree is 7, because the maximum exponent of y is 7.
Page No 124:
Question 4:
Classify the following polynomials as linear, quadratic, cubic and biquadratic polynomials:
(i) x + x2 + 4
(ii) 3x − 2
(iii) 2x + x2
(iv) 3y
(v) t2 + 1
(vi) 7t4 + 4t3 + 3t − 2
Answer:
(i)
The degree of the polynomial is 2. It is quadratic in x.
So, it is quadratic polynomial.
(ii)
The degree of the polynomial is 1. It is a linear polynomial in x.
(iii)
The degree of the polynomial is 1.
It is linear a polynomial in x.
(iv) 3y
The degree of the polynomial is 1. It is linear in y.
(v)
The degree of the polynomial is 2. It is quadratic polynomial in t.
(vi)
The degree of the polynomial is 4. Therefore, it is bi-quadratic polynomial in t.
Page No 124:
Question 5:
Classify the following polynomials as polynomials in one-variable, two variables etc.:
(i) x2 − xy + 7y2
(ii) x2 − 2tx + 7t2 − x + t
(iii) t3 − 3t2 + 4t − 5
(iv) xy + yz + zx
Answer:
(i)
Here, x and y are two variables.
So, it is polynomial in two variables.
(ii)
Here, x and t are two variables.
So, it is polynomial in two variables.
(iii)
Here, only t is variable.
So, it is polynomial in one variable.
(iv)
Here, x, y and z are three variables
So, it is polynomial in three variables.
Page No 124:
Question 6:
Identify polynomials in the following:
(i) f(x) = 4x3 − x2 − 3x + 7
(ii) g(x) = 2x3 − 3x2+ − 1
(iii) p(x) =
(iv) q(x) = 2x2 − 3x + + 2
(v) h(x) =
(vi) f(x) =
Answer:
(i)
It is cubic in x, so, it is cubic polynomial in x variable.
(ii)
Here, exponent of x in is not a positive integer, so, it is not a polynomial.
(iii)
It is a quadratic polynomial.
(iv) q(x) = 2x2 − 3x + + 2
Here, exponent of x in is not a positive integer. So it is not a polynomial.
(v)
Here, exponent of x in x3/2 is not a positive integer. So, it is not a polynomial.
(vi)
Here, exponent of x in is not a positive integer, so, it not a polynomial.
Page No 124:
Question 7:
Identify constant, linear, quadratic and cubic polynomials from the following polynomials:
(i) f(x) = 0
(ii) g(x) = 2x3 − 7x + 4
(iii) h(x) = -
(iv) p(x) = 2x2 − x + 4
(v) q(x) = 4x + 3
(vi) r(x) = 3x3 + 4x2 + 5x − 7
Answer:
(i)
The given expression is a Constant polynomial as there is no variable term in it.
(ii)
The given expression is Cubic polynomial as the highest exponent of x is 3.
(iii)
The given expression is linear polynomial as the highest exponent of x is 1.
(iv)
The given expression is Quadratic polynomial as the highest exponent of x is 2.
(v)
The given polynomial is an linear polynomial as the highest exponent of x is 1.
(vi)
The given polynomial is Cubic polynomial as the highest exponent of x is 3.
Page No 124:
Question 8:
Give one example each of a binomial of degree 35, and of a monomial of degree 100.
Answer:
An example of binomial of degree 35 is . It is a binomial as it has two terms and degree is 35 because highest exponent of t is 35.
An example of monomial of degree 100 is . It is a monomial as it has only one term and degree is 100 because highest exponent of x is 100
Page No 124:
Question 9:
For the polynomial , write the
(i) degree
(ii) coefficient of x3
(iii) coefficient of x6
(iv) constant term
Answer:
Given:
(i) Degree of polynomial is the highest degree of its terms.
Here, degree of is 6.
(ii) Coefficient of x3 is .
(iii) Coefficient of x6 is –1.
(iv) The constant term in the polynomial is .
Page No 124:
Question 10:
Write the coefficient of x2 in each of the following polynomials:
(i)
(ii) 3x – 5
(iii) (x – 1) (3x – 4)
(iv) (2x – 5) (2x2 – 3x + 1)
Answer:
(i) Coefficient of x2 in is 1.
(ii) Coefficient of x2 in 3x – 5 is 0.
(iii) (x – 1) (3x – 4) = 3x2 – 7x + 4
Coefficient of x2 in 3x2 – 7x + 4 is 3.
(iv) (2x – 5) (2x2 – 3x + 1) = 4x3 – 6x2 + 2x – 10x2 + 15x – 5
= 4x3 – 16x2 + 17x – 5
Coefficient of x2 in 4x3 – 16x2 + 17x – 5 is –16.
Page No 124:
Question 11:
Give an example of a polynomial, which is
(i) a monomial of degree 1
(ii) a binomial of degree 20
(iii) a trinomial of degree 2
Answer:
(i) A monomial has a single term and degree 1 means the highest power of the variable is 1.
Monomial of degree 1 : 5x
(ii) A binomial has two terms and degree 20 means the highest power of the variable is 20.
Binomial of degree 20 : 6y20 + 5
(iii) A tri-nomial has three terms and degree 2 means the highest power of the variable is 2.
Tri-nomial of degree 2 : x2 + x + 1
Page No 128:
Question 1:
If f(x) = 2x3 − 13x2 + 17x + 12, find (i) f(2) (ii) f(−3) (iii) f(0)
Answer:
Let be the given polynomial
(i) The value of f (2) can be found by putting x = 2
= 10
(ii) The value of f (–3) can be found by putting x = –3
(iii) The value of f (0) can be found by putting x = 0
Page No 128:
Question 2:
Verify whether the indicated numbers are zeros of the polynomials corresponding to them in the following cases:
(i)
(ii)
(iii)
(iv)
(v)
(vi)
(vii)
(viii)
Answer:
(i) To check whether the given number is the zero of the polynomial or not we have to find
Hence, is the zeros of the given polynomial.
(ii) To check whether the given number is the zero of the polynomial or not we have to find and
Now,
And ,
Hence, and x = 1 are the zeros of the polynomial.
(iii) To check whether the given number is the zero of the polynomial or not we have to find
Now,
And
Here, both the value of , are not satisfied the polynomial. Therefore, they are not the zeros of the polynomial.
(iv) To check whether the given number is the zero of the polynomial or not we have to find
And
Hence, x = 1, 2, 3 are the zeros of the polynomial p(x).
(v)To check whether the given number is the zero of the polynomial or not we have to find
Here, , does not satisfy therefore, is not a zero of the polynomial.
(vi)To check whether the given number is the zero of the polynomial or not we have to find
Hence, x = 0 is the zeros of the polynomial.
(vii) To check whether the given number is the zero of the polynomial or not we have to find
Hence, is zeros of the polynomial.
(viii)To check whether the given number is the zero of the polynomial or not we have to find
Hence, does not satisyf the polynomial, so, is not zero of the polynomial.
Page No 128:
Question 3:
If x = 2 is a root of the polynomial f(x) = 2x2 − 3x + 7a, find the value of a.
Answer:
The given polynomial is
If x = 2 is the root of the polynomial.
Then
Page No 128:
Question 4:
If is a zero of the polynomial p(x) = 8x3 − ax2−x + 2, find the value of a.
Answer:
The given polynomial is
If is a zeros of the polynomial p(x).
then
Therefore,
Hence the value of
Page No 128:
Question 5:
If x = 0 and x = −1 are the roots of the polynomial f(x) =2x3 − 3x2+ ax + b, find the value of a and b.
Answer:
The given polynomial is
f(x) =2x3 − 3x2 + ax + b
If is zeros of the polynomial f(x), then f(0) = 0
Similarly, if x = − 1 is the zeros of the polynomial of,
Then,
Putting the value of b from equation (1)
Thus,
Page No 129:
Question 6:
Find the integral roots of the polynomial f(x) = x3 + 6x2 + 11x + 6.
Answer:
The given polynomial is
Here, f(x) is a polynomial with integer coefficient and the coefficient of highest degree term is 1. So, the integer roots of f(x) are factors of 6. Which are by observing.
= 0
Also,
And similarly,
f(−3) = 0
Therefore, the integer roots of the polynomial f(x) are −1, −2, − 3
Page No 129:
Question 7:
Find rational roots of the polynomial f(x) = 2x3 + x2 − 7x − 6.
Answer:
The given polynomial is
f(x) is a cubic polynomial with integer coefficients. If is rational root in lowest terms, then the values of b are limited
to the factors of 6 which are and the values of c are limited to the factor of 2 as . Hence, the possible
rational roots are .
Since,
So, 2 is a root of the polynomial
Now, the polynomial can be written as,
Also,
Therefore,
Hence, the rational roots of the polynomialare 2, – 3/2 and – 1.
Page No 133:
Question 1:
In each of the following, using the remainder theorem, find the remainder when f(x) is divided by g(x) and verify the result by actual division: (1−8)
1. f(x) = x3 + 4x2 − 3x + 10, g(x) = x + 4
Answer:
Let us denote the given polynomials as
We have to find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
Now we will show by actual division
So the remainder by actual division is 22
Page No 133:
Question 2:
f(x) = 4x4 − 3x3 − 2x2 + x − 7, g(x) = x − 1
Answer:
Let us denote the given polynomials as
We have to find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
Now we will show remainder by actual division
So the remainder by actual division is −7
Page No 133:
Question 3:
f(x) = 2x4 − 6x3 + 2x2 − x + 2, g(x) = x + 2
Answer:
Let us denote the given polynomials as
We have to find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
Now we will calculate the remainder by actual division
So the remainder by actual division is 92
Page No 133:
Question 4:
f(x) = 4x3 − 12x2 + 14x − 3, g(x) = 2x − 1
Answer:
Let us denote the given polynomials as
We have to find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
Now we will calculate the remainder by actual division
So the remainder by actual division is
Page No 133:
Question 5:
f(x) = x3 − 6x2 + 2x − 4, g(x) = 1 − 2x
Answer:
Let us denote the given polynomials as
We have to find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
Now we will calculate remainder by actual division
So the remainder is
Page No 133:
Question 6:
f(x) = x4 − 3x2 + 4, g(x) = x − 2
Answer:
Let us denote the given polynomials as
We have to find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
We will calculate remainder by actual division
So the remainder is 8
Page No 133:
Question 7:
f(x) = 9x3 − 3x2 + x − 5, g(x) =
Answer:
Let us denote the given polynomials as
We have to find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
Remainder by actual division
Remainder is −3
Page No 134:
Question 8:
Answer:
Let us denote the given polynomials as
We have to find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
Remainder by actual division
Remainder is 0
Page No 134:
Question 9:
Find the remainder when x3 + 3x2 + 3x + 1 is divided by
(i) x + 1
(ii)
(iii) x
(iv)
(v) 5 + 2x
Answer:
Let us denote the given polynomials as
(i) We will find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
(ii) We will find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
(iii) We will find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
(iv) We will find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
(v) We will find the remainder whenis divided by.
By the remainder theorem, whenis divided bythe remainder is
Page No 134:
Question 10:
If the polynomials 2x3 + ax2 + 3x − 5 and x3 + x2 − 4x +a leave the same remainder when divided by x −2, find the value of a.
Answer:
Let us denote the given polynomials as
Now, we will find the remaindersandwhenandrespectively are divided by.
By the remainder theorem, whenis divided bythe remainder is
By the remainder theorem, whenis divided bythe remainder is
By the given condition, the two remainders are same. Then we have,
Page No 134:
Question 11:
If the polynomials ax3 + 3x2 − 13 and 2x3 − 5x + a, when divided by (x − 2) leave the same remainder, find the value of a.
Answer:
Let us denote the given polynomials as
Now, we will find the remaindersandwhenandrespectively are divided by.
By the remainder theorem, whenis divided bythe remainder is
By the remainder theorem, whenis divided bythe remainder is
By the given condition, the two remainders are same. Then we have, R1 = R2
Page No 134:
Question 12:
The polynomial when divided by x + 1 leaves the remainder 19. Find the values of a. Also, find the remainder when p(x) is divided by (x + 2).
Answer:
Given: p(x) = x4 – 2x3 + 3x2 – ax + 3a – 7
when p(x) is divided by (x + 1), remainder is 19.
By Remainder Theorem, we have
p(–1) = 19
⇒ (–1)4 – 2(–1)3 + 3(–1)2 – a(–1) + 3a – 7 = 19
⇒ 1 + 2 + 3 + a + 3a – 7 = 19
⇒ 4a – 1 = 19
⇒4a = 20
⇒a = 5
Thus, the value of a is 5.
Therefore, p(x) = x4 – 2x3 + 3x2 – 5x + 8
Now, when p(x) is divided by (x + 2), remainder will be p(–2)
∴ p(–2) = (–2)4 – 2(–2)3 + 3(–2)2 –5(–2) + 8
= 16 + 16 + 12 + 10 + 8
= 62
Hence, the remainder of polynomial p(x) when divided by (x + 2) is 62.
Page No 134:
Question 13:
The polynomials ax3 + 3x2 − 3 and 2x3 − 5x + a when divided by (x − 4) leave the remainders R1 and R2 respectively. Find the values of a in each of the following cases, if
(a) R1 = R2
(b) R1 + R2 = 0
(c) 2R1 − R2 = 0
Answer:
Let us denote the given polynomials as
Now, we will find the remaindersandwhenandrespectively are divided by.
By the remainder theorem, whenis divided bythe remainder is
By the remainder theorem, whenis divided bythe remainder is
(i) By the given condition,
R1 = R2
(ii) By the given condition,
R1 + R2 = 0
(iii) By the given condition,
2R1 − R2 = 0
Page No 141:
Question 1:
In each of the following, use factor theorem to find whether polynomial g(x) is a factor of polynomial f(x) or, not: (1−7)
f(x) = x3 − 6x2 + 11x − 6; g(x) = x − 3
Answer:
Given that:
By the factor theorem,
If g(x) is a factor of f(x)
i.e.
Then
As is zero therefore g(x), is the factor of polynomial f(x).
Page No 141:
Question 2:
f(x) = 3x4 + 17x3 + 9x2 − 7x − 10; g(x) = x + 5
Answer:
It is given that and
By the factor theorem, g(x) is a factor of polynomial f(x)
i.e.
Therefore,
Hence, g(x) is the factor of polynomial f(x).
Page No 141:
Question 3:
f(x) = x5 + 3x4 − x3 − 3x2 + 5x + 15, g(x) = x + 3
Answer:
It is given that and
By the factor theorem, g(x) is the factor of polynomial f(x).
i.e.
f (−3) = 0
Hence, g(x) is the factor of polynomial f (x).
Page No 141:
Question 4:
f(x) = x3 −6x2 − 19x + 84, g(x) = x − 7
Answer:
It is given that and
By the factor theorem, g(x) is the factor of polynomial f(x), if f (7) = 0.
Therefore, in order to prove that (x − 7) is a factor of f(x).
It is sufficient to show that f(7) = 0
Now,
Hence, (x − 7) is a factor of polynomial f(x).
Page No 141:
Question 5:
f(x) = 3x3 + x2 − 20x +12, g(x) = 3x − 2
Answer:
It is given that and
By the factor theorem,
(3x − 2) is the factor of f(x), if
Therefore,
In order to prove that (3x − 2) is a factor of f(x).
It is sufficient to show that
Now,
Hence, (3x − 2) is the factor of polynomial f(x).
Page No 141:
Question 6:
f(x) = 2x3 − 9x2 + x + 12, g(x) = 3 − 2x
Answer:
It is given that and
By factor theorem, (3 − 2x) is the factor of f(x), if = 0
Therefore,
In order to prove that (3 − 2x) is a factor of f(x). It is sufficient to show that
Now,
Hence, (3 − 2x), is the factor of polynomial f(x).
Page No 141:
Question 7:
f(x) = x3 − 6x2 + 11x − 6, g(x) = x2 − 3x + 2
Answer:
It is given that and
We have
and (x − 1) are factor of g(x) by the factor theorem.
To prove that (x − 2) and (x − 1) are the factor of f(x).
It is sufficient to show that f(2) and f(1) both are equal to zero.
And
Hence, g(x) is the factor of the polynomial f(x).
Page No 141:
Question 8:
Show that (x − 2), (x + 3) and (x − 4) are factors of x3 − 3x2 − 10x + 24.
Answer:
Let be the given polynomial.
By factor theorem,
and are the factor of f(x).
If and f(4) are all equal to zero.
Now,
also
And
Hence, and are the factor of polynomial f(x).
Page No 141:
Question 9:
Show that (x + 4) , (x − 3) and (x − 7) are factors of x3 − 6x2 − 19x + 84
Answer:
Let be the given polynomial.
By the factor theorem,
and are the factor of f(x).
If and f(7) are all equal to zero.
Therefore,
Also
And
Hence, and are the factor of the polynomial f(x).
Page No 141:
Question 10:
For what value of a is (x − 5) a factor of x3− 3x2 + ax − 10?
Answer:
Let be the given polynomial.
By factor theorem, is the factor of f(x), if f (5) = 0
Therefore,
Hence, a = − 8.
Page No 141:
Question 11:
Find the value of a such that (x − 4) is a factors of 5x3 − 7x2 − ax − 28.
Answer:
Let be the given polynomial.
By the factor theorem,
(x − 4) is a factor of f(x).
Therefore f(4) = 0
Hence ,
Hence,
Page No 141:
Question 12:
Find the value of a, if x + 2 is a factor of 4x4 + 2x3 − 3x2 + 8x + 5a.
Answer:
Let 4x4 + 2x3 − 3x2 + 8x + 5a be the polynomial.
By the factor theorem,
is a factor of f(x) if f(−2) = 0.
Therefore,
Hence,
Page No 141:
Question 13:
Find the value k if x − 3 is a factor of k2x3 − kx2 + 3kx − k.
Answer:
Let be the given polynomial.
By the factor theorem,
(x − 3) is a factor of f(x) if f (3) = 0
Therefore,
Hence, the value of k is 0 or .
Page No 141:
Question 14:
If x − 2 is a factor of each of the following two polynomials, find the values of a in each case
(i) x3 − 2ax2 + ax − 1
(ii) x5 − 3x4 − ax3 + 3ax2 + 2ax + 4
Answer:
(i) Let be the given polynomial.
By factor theorem, if (x − 2) is a factor of f(x), then f (2) = 0
Therefore,
Thus the value of a is 7/6.
(ii) Let f(x) = x5 − 3x4 − ax3 + 3ax2 + 2ax + 4 be the given polynomial.
By the factor theorem, (x − 2) is a factor of f(x), if f (2) = 0
Therefore,
Thus, the value of a is .
Page No 141:
Question 15:
For what value of m is x3 – 2mx2 + 16 is divisible by (x + 2)?
Answer:
Let p(x) = x3 – 2mx2 + 16
Since, p(x) is divisible by (x + 2).
∴ p(–2) = 0 (By remainder theorem)
⇒ (–2)3 – 2m(–2)2 + 16 = 0
⇒ –8 – 8m + 16 = 0
⇒ 8m = 8
⇒ m = 1
Hence, the value of m is 1.
Page No 141:
Question 16:
Find the value of m so that 2x – 1 be a factor of 8x4 + 4x3 – 16x2 + 10x + m.
Answer:
Let p(x) = 8x4 + 4x3 – 16x2 + 10x + m and g(x) = 2x – 1
g(x) = 0
⇒ x =
For g(x) to be a factor of p(x),
Hence, the value of m is –2.
Page No 141:
Question 17:
If x + 1 is a factor of ax3 + x2 – 2x + 4a – 9, find the value of a.
Answer:
Given: p(x) = ax3 + x2 – 2x + 4a – 9
g(x) = x + 1
⇒ x + 1 = 0
⇒ x = –1
If g(x) is a factor of p(x), then p(–1) = 0.
⇒ a(–1)3 + (–1)2 – 2(–1) + 4a – 9 = 0
⇒ –a + 1 + 2 + 4a – 9 = 0
⇒ 3a – 6 = 0
⇒ a = 2
Hence, the value of a is 2.
Page No 141:
Question 18:
Find the values of a and b, if (x2 − 4) is a factor of ax4 + 2x3 − 3x2 + bx − 4
Answer:
Let and be the given polynomial.
We have,
are the factors of g(x).
By factor theorem, if and both are the factor of f(x)
Then f(2) and f(−2) are equal to zero.
Therefore,
and
Adding these two equations, we get
Putting the value of a in equation (i), we get
Hence, the value of a and b are 1, − 8 respectively.
Page No 141:
Question 19:
Find α and β, if (x + 1) and (x + 2) are factors of x3 + 3x2− 2αx + β.
Answer:
Let be the given polynomial.
By the factor theorem, and are the factor of the polynomial f(x) if and both are equal to zero.
Therefore,
and
Subtracting (i) from (ii)
We get,
Putting the value of in equation (i), we get
Hence, the value of α and β are −1, 0 respectively.
Page No 142:
Question 20:
In each of the following two polynomials, find the value of a, if (x − a) is factor:
(i) x6 − ax5 + x4 − ax3 + 3x − a + 2
(ii x5 − a2x3 + 2x + a + 1)
Answer:
(i) Let be the given polynomial.
By factor theorem, (x − a) is a factor of the polynomial if f(a) = 0
Therefore,
Thus, the value of a is − 1.
(ii) Let be the given polynomial.
By factor theorem, (x − a) is a factor of f(x), if f(a) = 0.
Therefore,
Thus, the value of a is − 1/3.
Page No 142:
Question 21:
In each of the following two polynomials, find the value of a, if (x + a) is a factor.
(i) x3 + ax2 − 2x +a + 4
(ii) x4 − a2x2 + 3x −a
Answer:
(i) Let be the given polynomial.
By the factor theorem, (+ a) is the factor of f(x), if f(− a) = 0, i.e.,
Thus, the value of a is − 4/3.
(ii) Let be the polynomial. By factor theorem, (x + a) is a factor of the f(x), if f(− a) = 0, i.e.,
Thus, the value of a is 0.
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Question 22:
Find the values of p and q so that x4 + px3 + 2x2 − 3x + q is divisible by (x2 − 1).
Answer:
Let and be the given polynomials.
We have,
Here, are the factor of g(x).
If f(x) is divisible by and , then and are factor of f(x).
Therefore, f(1) and f(−1) both must be equal to zero.
Therefore,
and
Adding both the equations, we get,
Putting this value in (i)
Hence, the value of p and q are 3, −3 respectively.
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Question 23:
Find the values of a and b so that (x + 1) and (x − 1) are factors of x4 + ax3 − 3x2 + 2x + b.
Answer:
Let be the given polynomial.
By factor theorem, and are the factors of f(x) if f(−1) and f(1) both are equal to zero.
Therefore,
and
Adding equation (i) and (ii), we get
Putting this value in equation (i), we get,
Hence, the value of a and b are – 2 and 2 respectively.
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Question 24:
If x3 + ax2 − bx+ 10 is divisible by x2 − 3x + 2, find the values of a and b.
Answer:
Let and be the given polynomials.
We have,
Here, and are the factors of g(x),
Now,
By factor theorem,
and
Subtracting (ii) by (i), we get,
Putting this value in equation (ii), we get,
Hence, the value of a and b are 2 and 13 respectively.
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Question 25:
If both (x + 1) and (x − 1) are factors of ax3 + x2 − 2x + b, find the values of a and b.
Answer:
Let be the given polynomial.
By factor theorem, if and both are factors of the polynomial f (x). if f(−1) and f(1) both are equal to zero.
Therefore,
And
Adding (i) and (ii), we get
And putting this value in equation (ii), we get,
a = 2
Hence, the value of a and b are 2 and −1 respectively.
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Question 26:
What must be subtracted from x3 − 6x2 − 15x + 80 so that the result is exactly divisible by x2 + x − 12?
Answer:
By divisible algorithm, when is divided by the reminder is a linear polynomial
Let be subtracted from p(x) so that the result is divisible by q(x).
Let
We have,
Clearly, and are factors of q(x), therefore, f(x) will be divisible by q(x) if and are factors of f(x), i.e. f (−4) and f (3) are equal to zero.
Therefore,
and
Adding (i) and (ii), we get,
Putting this value in equation (i), we get,
Hence, will be divisible by if 4 x − 4 is subtracted from it
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Question 27:
What must be added to 3x3 + x2 − 22x + 9 so that the result is exactly divisible by 3x2 + 7x − 6?
Answer:
By division algorithm, when is divided by the reminder is a linear polynomial. So, let r(x) = ax + b be added to p(x) so that the result is divisible by q(x)
Let
We have,
Clearly, and are factors of q(x).
Therefore, f(x) will be divisible by q(x) if and are factors of f(x), i.e.,
and f(−3) are equal to zero.
Now,
And
Substituting the value of b from (ii) in (i), we get,Now, from (ii), we get
So, we have a = 2 and b = 3
Hence, p(x) is divisible by q(x), if is added to it.
Page No 148:
Question 1:
Using factor theorem, factorize each of the following polynomials:
x3 + 6x2 + 11x + 6
Answer:
Let f(x) = x3 + 6x2 + 11x + 6 be the given polynomial.
Now, put the we get
Therefore, is a factor of f(x).
Now,
Hence, are the factors of f(x).
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Question 2:
x3 + 2x2 − x − 2
Answer:
Let be the given polynomial.
Now, put the x = -1, we get
Therefore, is a factor of polynomial f(x).
Now, x3 + 2x2 − x − 2 can be written as,
Hence, are the factors of the polynomial f(x).
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Question 3:
x3 − 6x2 + 3x + 10
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Hence, are the factors of the polynomial f(x).
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Question 4:
x4 − 7x3+ 9x2 + 7x − 10
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Where
Putting we get
Therefore, is a factor of g(x).
Now,
From equation (i) and (ii), we get
Hence are the factors of polynomial f(x).
Page No 148:
Question 5:
3x3 − x2 − 3x + 1
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Hence are the factors of polynomial f(x).
Page No 148:
Question 6:
x3 − 23x2 + 142x − 120
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Hence are the factors of polynomial f(x).
Page No 148:
Question 7:
y3 − 7y + 6
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(y).
Now,
Hence are the factors of polynomial f (y).
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Question 8:
x3 − 10x2 − 53x − 42
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Hence are the factors of polynomial f(x).
Page No 148:
Question 9:
y3 − 2y2 − 29y − 42
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(y).
Now,
Hence are the factors of polynomial f(y).
Page No 148:
Question 10:
2y3 − 5y2 − 19y + 42
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(y).
Now,
Hence are the factors of polynomial f(y).
Page No 148:
Question 11:
x3 + 13x2 + 32x + 20
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Hence are the factors of polynomial f(x).
Page No 148:
Question 12:
x3 − 3x2 − 9x − 5
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Hence are the factors of polynomial f(x).
Page No 148:
Question 13:
2y3 + y2 − 2y − 1
Answer:
Let be the given polynomial.
Now, putting we get
Now,
Hence are the factors of polynomial f(y).
Page No 148:
Question 14:
x3 − 2x2 − x + 2
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Hence are the factors of polynomial f(x).
Page No 148:
Question 15:
x4 − 2x3 − 7x2 + 8x + 12
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Where
Putting we get
Therefore, is the factor of g(x).
Now,
From equation (i) and (ii), we get
Hence are the factors of polynomial f(x).
Page No 148:
Question 16:
x4 + 10x3 + 35x2 + 50x + 24
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Where
Putting we get
Therefore, is the factor of g(x).
Now,
From equation (i) and (ii), we get
Hence are the factors of polynomial f(x).
Page No 148:
Question 17:
2x4 − 7x3 − 13x2 + 63x − 45
Answer:
Let be the given polynomial.
Now, putting we get
Therefore, is a factor of polynomial f(x).
Now,
Where
Putting we get
Therefore, is a factor of g(x).
Now,
From equation (i) and (ii), we get
Hence are the factors of polynomial f(x).
Page No 148:
Question 18:
Factorize each of the following polynomials:
(i) x3 + 13x2 + 31x − 45 given that x + 9 is a factor
(ii) 4x3 + 20x2 + 33x + 18 given that 2x + 3 is a factor.
Answer:
(i) Let be the given polynomial.
is a factor of the polynomial f(x).
Now,
Hence are the factors of polynomial f(x).
(ii) Let be the given polynomial.
Therefore is a factor of the polynomial f(x).
Now,
Hence are the factors of polynomial f(x).
Page No 149:
Question 1:
Define zero or root of a polynomial.
Answer:
A real number a is a zero (or root) of the polynomial f(x), if f (a) = 0
Page No 149:
Question 2:
If is a zero of the polynomial f(x) = 8x3 + ax2 − 4x + 2, find the value of a.
Answer:
Since is a zero of polynomial f(x).
Therefore
The value of a is .
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Question 3:
Write the remainder when the polynomial f(x) = x3 + x2 − 3x + 2 is divided by x + 1.
Answer:
When the polynomial f(x), divided by the remainder will be
Thus, the reminder = 5
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Question 4:
Find the remainder when x3 + 4x2 + 4x − 3 is divided by x.
Answer:
When the polynomial f(x) = x3 + 4x2 + 4x − 3 is divided by x the remainder will be.
Thus, the reminder = −3
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Question 5:
If x + 1 is a factor of x3 + a, then write the value of a.
Answer:
As is a factor of polynomial
i.e.
Thus, the value of a = 1
Page No 149:
Question 6:
If f(x) = x4 − 2x3 + 3x2 − ax − b when divided by x − 1, the remainder is 6, then find the value of a + b
Answer:
When polynomial divided by
The remainder is 6.
i.e.
Thus, the value of
Page No 149:
Question 1:
7 – 9x + 2x2 is called a _________ polynomial.
Answer:
Polynomial with degree 2 is known as a quadratic polynomial.
Hence, 7 – 9x + 2x2 is called a quadratic polynomial.
Page No 149:
Question 2:
12x – 7x2 + 4 – 2x3 is called a ___________ polynomial.
Answer:
Polynomial with degree 3 is known as a cubic polynomial.
âHence, 12x – 7x2 + 4 – 2x3 is called a cubic polynomial.
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Question 3:
13x2 – 88x3 + 9x4 is called a _________ polynomial.
Answer:
Polynomial with degree 4 is known as a biquadratic polynomial.
âHence, 12x – 7x2 + 4 – 2x3 is called a biquadratic polynomial.
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Question 4:
If x + 1 is a factor of the polynomial ax3 + x2 – 2x + 4a – 9, then a = __________.
Answer:
Let f(x) = ax3 + x2 – 2x + 4a – 9
It is given that one factor of f(x) is (x + 1).
Therefore, .
On putting x = –1 in f(x) = 0, we get
Hence, if x + 1 is a factor of the polynomial ax3 + x2 – 2x + 4a – 9, then a = 2.
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Question 5:
If 3x – 1 is a factor of the polynomial 81x3 – 45x2 +3a – 6, then the value of a is ___________.
Answer:
Let f(x) = 81x3 – 45x2 +3a – 6
It is given that one factor of f(x) is (3x – 1).
Therefore, .
On putting x = in f(x) = 0, we get
Hence, if 3x – 1 is a factor of the polynomial 81x3 – 45x2 +3a – 6, then the value of a is
Page No 149:
Question 6:
The remainders obtained when x3 + x2 – 9x – 9 is divided by x, x + 1 and x + 2 respectively are _________.
Answer:
Let f(x) = x3 + x2 – 9x – 9
To find the remainder obtained when x3 + x2 – 9x – 9 is divided by x,
we use remainder theorem, put x = 0.
f(0) is the remainder.
Now,
f(0) = (0)3 + (0)2 – 9(0) – 9
= –9
Hence, the remainder obtained when x3 + x2 – 9x – 9 is divided by x is –9.
To find the remainder obtained when x3 + x2 – 9x – 9 is divided by x + 1,
put x +1 = 0.
f(–1) is the remainder.
Now,
f(–1) = (–1)3 + (–1)2 – 9(–1) – 9
= –1 + 1 + 9 – 9
= 0
Hence, the remainder obtained when x3 + x2 – 9x – 9 is divided by x + 1 is 0.
To find the remainder obtained when x3 + x2 – 9x – 9 is divided by x + 2,
put x +2 = 0.
f(–2) is the remainder.
Now,
f(–2) = (–2)3 + (–2)2 – 9(–2) – 9
= –8 + 4 + 18 – 9
= 5
Hence, the remainder obtained when x3 + x2 – 9x – 9 is divided by x + 2 is 5.
Hence, the remainders obtained when x3 + x2 – 9x – 9 is divided by x, x + 1 and x + 2 respectively are –9, 0 and 5.
Page No 149:
Question 7:
The remainder when f(x) = 4x3 – 3x2 + 2x – 1 is divided by 2x + 1 is __________.
Answer:
Let f(x) = 4x3 – 3x2 + 2x – 1
To find the remainder obtained when 4x3 – 3x2 + 2x – 1 is divided by 2x + 1,
we use remainder theorem, put 2x + 1 = 0.
f() is the remainder.
Now,
Hence, the remainder when f(x) = 4x3 – 3x2 + 2x – 1 is divided by 2x + 1 is
Page No 149:
Question 8:
The degree of a polynomial f(x) is 7 and that of polynomial f(x) g(x) is 56, then degree of g(x) is ________.
Answer:
Given:
Degree of a polynomial f(x) = 7
Degree of polynomial f(x) g(x) = 56
Degree of polynomial f(x) g(x) = Degree of âpolynomial f(x) × Degree of âpolynomial g(x)
⇒ 56 = 7 × Degree of âpolynomial g(x)
⇒ Degree of âpolynomial g(x) =
⇒ Degree of âpolynomial g(x) = 8
Hence, degree of g(x) is 8.
Page No 149:
Question 9:
The remainder when x15 is divided by x + 1 is __________.
Answer:
Let f(x) = x15
To find the remainder obtained when x15 is divided by x + 1,
we use remainder theorem, put x + 1 = 0.
f(−1) is the remainder.
Now,
Hence, the remainder when x15 is divided by x + 1 is −1.
Page No 150:
Question 10:
If
Answer:
Let p(x) = x2 – 4x + 3
Hence, if
Page No 150:
Question 11:
If the polynomial f(x) = 5x5 – 3x3 + 2x2 – k gives remainder 1 when divided by x + 1, then k = __________.
Answer:
Let f(x) = 5x5 – 3x3 + 2x2 – k
To find the remainder obtained when 5x5 – 3x3 + 2x2 – k is divided by x + 1,
we use remainder theorem, put x + 1 = 0.
f(−1) is the remainder.
Now,
Hence, k = –1.
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Question 12:
The remainder when f(x) = x45 is divided by x2 – 1 is ____________.
Answer:
Let f(x) = x45
To find the remainder obtained when x45 is divided by x2 – 1,
Let the remainder (r) be ax + b.
Then,
f(x) = (x2 – 1) q + r
Therefore, the remainder (r) = 1(x) + 0 = x.
Hence, the remainder when f(x) = x45 is divided by x2 – 1 is x.
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