NCERT solutions class 9 maths chapter 2 â€“ Polynomials are provided here. These NCERT solutions are created by the BYJUâ€™S expert faculties to help students in the preparation of their board exams. These expert faculties solve and provide the NCERT maths solution so that it should help students to solve the problems comfortably. They give a detailed and stepwise explanation of each answer to the problems given in the exercises in the NCERT textbook for class 9.

In CBSE class 9 Polynomials chapter, students are introduced to a lot of important topics which will be helpful for those who wish to pursue mathematics as a subject in further classes. Based on these NCERT solutions. These solutions help students to prepare for their upcoming Board Exams by covering the whole the syllabus which follows NCERT guidelines.

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## Exercise 2.1 Page: 32

**Q1. Which of the following expressions are polynomials in one variable and which are not? State reasons for your answer.****(i) 4x ^{2} â€“ 3x + 7**

Solution:

The equation 4x^{2} â€“ 3x + 7 can be written as 4x^{2} â€“ 3x^{1} + 7x^{0}

Since *x* is the only variable in the given equation and the powers of x (i.e., 2, 1 and 0) are whole numbers, we can say that the expression 4x^{2} â€“ 3x + 7 is a polynomial in one variable.

**(ii) y ^{2} + âˆš2**

Solution:

The equation y^{2} + can be written as y^{2} + y^{0}

Since *y* is the only variable in the given equation and the powers of y (i.e., 2 and 0) are whole numbers, we can say that the expression y^{2} + is a polynomial in one variable.

**(iii) 3âˆšt + tâˆš2 **

Solution:

The equation 3 + t can be written as

Though, *t* is the only variable in the given equation, the powers of *t* (i.e.,) is not a whole number. Hence, we can say that the expression 3 + t is **not **a polynomial in one variable.

**(iv) y + 2/y**

Solution:

The equation y + can be written as y+2y^{-1}

Though, *y *is the only variable in the given equation, the powers of *y* (i.e.,-1) is not a whole number. Hence, we can say that the expression y + is **not **a polynomial in one variable.

**(v) x ^{10} + y^{3} + t^{50}**

Solution:

Here, in the equation x^{10} + y^{3} + t^{50}

Though, the powers, 10, 3, 50, are whole numbers, there are 3 variables used in the expression

x^{10} + y^{3} + t^{50}. Hence, it is **not **a polynomial in one variable.

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**Q2. Write the coefficients of x ^{2} in each of the following:**

**(i) 2 + x**

^{2}+ xSolution:

The equation 2 + x^{2} + x can be written as 2 + (1) x^{2} + x

We know that, coefficient is the number which multiplies the variable.

Here, the number that multiplies the variable x^{2} is 1

, the coefficients of x^{2 }in 2 + x^{2} + x is 1.

**(ii) 2 â€“ x ^{2} + x^{3}**

Solution:

The equation 2 â€“ x^{2} + x^{3 }can be written as 2 + (â€“1) x^{2} + x^{3}

We know that, coefficient is the number (along with its sign,i.e., â€“ or +) which multiplies the variable.

Here, the number that multiplies the variable x^{2} is -1

, the coefficients of x^{2 }in 2 â€“ x^{2} + x^{3 }is -1.

**(iii) Î /2 x ^{2 }+x**

Solution:

The equation Î /2x^{2 }+x^{}can be written as (Î /2 ) x^{2} + x

We know that, coefficient is the number (along with its sign,i.e., â€“ or +) which multiplies the variable.

Here, the number that multiplies the variable x^{2} is

, the coefficients of x^{2 }in Î /2x^{2 }+x is Î /2.

**(iv)âˆš2x-1**

Solution:

The equationxâˆš2x-1^{}can be written as 0x^{2 }+âˆš2x-1 [Since 0x^{2} is 0]

We know that, coefficient is the number (along with its sign,i.e., â€“ or +) which multiplies the variable.

Here, the number that multiplies the variable x^{2} is 0

, the coefficients of x^{2 }inâˆš2x-1 is 0.

Â **Q3. Give one example each of a binomial of degree 35, and of a monomial of degree 100.**

Solution:

Binomial of degree 35: A polynomial having two terms and the highest degree 35 is called a binomial of degree 35

Eg., Â 3x^{35}+5

Monomial of degree 100: A polynomial having one term and the highest degree 100 is called a monomial of degree 100

Eg., Â 4x^{100}

Â **Q4. Write the degree of each of the following polynomials:****(i) 5x ^{3} + 4x^{2} + 7x**

Solution:

The highest power of the variable in a polynomial is the degree of the polynomial.

Here, 5x^{3} + 4x^{2} + 7x= 5x^{3} + 4x^{2} + 7x^{1}

The powers of the variable x are: 3, 2, 1

, the degree of 5x^{3} + 4x^{2} + 7x is 3 as 3 is the highest power of x in the equation.

**(ii) 4 â€“ y ^{2}**

Solution:

The highest power of the variable in a polynomial is the degree of the polynomial.

Here, in 4 â€“ y^{2},

The power of the variable y is: 2

, the degree of 4 â€“ y^{2} is 2 as 2 is the highest power of y in the equation.

**(iii) 5t â€“ âˆš7**

Solution:

The highest power of the variable in a polynomial is the degree of the polynomial.

Here, in 5t â€“ âˆš7,

The power of the variable y is: 1

, the degree of 5t â€“ âˆš7 is 1 as 1 is the highest power of y in the equation.

**(iv) 3**

Solution:

The highest power of the variable in a polynomial is the degree of the polynomial.

Here, 3== 3x^{0}

The power of the variable here is: 0

, the degree of 3 is 0.

Â **Q5. Classify the following as linear, quadratic and cubic polynomials:**

Solution:

We know that,

Linear polynomial: A polynomial of degree one is called a linear polynomial.

Quadratic polynomial: A polynomial of degree two is called a quadratic polynomial.

Cubic polynomial: A polynomial of degree three a cubic polynomial.

**(i) x ^{2} + x**

Solution:

The highest power of x^{2} + x is 2

, the degree is 2

Hence, x^{2} + x is a quadratic polynomial

**(ii) x â€“ x ^{3}**

Solution:

The highest power of x â€“ x^{3 }is 3

, the degree is 3

Hence, x â€“ x^{3} is a cubic polynomial

**(iii) y + y ^{2} + 4**

Solution:

The highest power of y + y^{2} + 4 is 2

, the degree is 2

Hence, y + y^{2} + 4 is a quadratic polynomial

**(iv) 1 + x**

Solution:

The highest power of 1 + x is 1

, the degree is 1

Hence, 1 + x is a linear polynomial

**(v) 3t**

Solution:

The highest power of 3t is 1

, the degree is 1

Hence, 3t is a linear polynomial

**(vi) r ^{2}**

Solution:

The highest power of r^{2} is 2

, the degree is 2

Hence, r^{2} is a quadratic polynomial

**(vii) 7x ^{3}**

Solution:

The highest power of 7x^{3 }is 3

, the degree is 3

Hence, 7x^{3} is a cubic polynomial

Â

## Exercise 2.2 Page: 34

Â **Q1. Find the value of the polynomial (x)=5xâˆ’4x ^{2}+3Â **

**(i) x= 0**

**(ii) xÂ = â€“ 1**

**(iii) xÂ = 2**

Solution:

LetÂ f(x)= 5xâˆ’4x^{2}+3Â

(i)Â When x=0

f(0)=5(0)+4(0)^{2}+3

=3

(ii)Â When x= -1

f(x)=5xâˆ’4x^{2}+3

f(âˆ’1)=5(âˆ’1) âˆ’4(âˆ’1)^{2}+3

=âˆ’5â€“4+3

=âˆ’6Â

(iii)Â When x=2

f(x)=5xâˆ’4x^{2}+3

f(2)=5(2) âˆ’4(2)^{2}+3

=10â€“16+3

=âˆ’3

Â **Q2. FindÂ p(0),Â p(1) andÂ p(2) for each of the following polynomials:****(i) p(y)=y ^{2}âˆ’y+1**

Solution:

p(y)=y^{2}â€“y+1

âˆ´p(0)=(0)^{2}âˆ’(0)+1=1

p(1)=(1)^{2}â€“(1)+1=1

p(2)=(2)^{2}â€“(2)+1=3

**(ii) p(t)=2+t+2t ^{2}âˆ’t^{3}**

Solution:

p(t)= 2+t+2t^{2}âˆ’t^{3}

âˆ´p(0)=2+0+2(0)^{2}â€“(0)^{3}=2

p(1)=2+1+2(1)^{2}â€“(1)^{3}=2+1+2â€“1=4

p(2)=2+2+2(2)^{2}â€“(2)^{3}=2+2+8â€“8=4

**(iii) p(x)=x ^{3}**

Solution:

p(x)=x^{3}

âˆ´p(0)=(0)^{3}=0

p(1)=(1)^{3}=1

p(2)=(2)^{3}=8

**(iv) p(x)=(xâˆ’1)(x+1)**

Solution:

p(x)=(xâ€“1)(x+1)

âˆ´p(0)=(0â€“1)(0+1)=(âˆ’1)(1)=â€“1

p(1)=(1â€“1)(1+1)=0(2)=0

p(2)=(2â€“1)(2+1)=1(3)=3

Â **Q3. Verify whether the following are zeroes of the polynomial, indicated against them.****(i) p(x)=3x+1, x=âˆ’1/3**

Solution:

For,Â x=âˆ’1/3Â , p(x)=3x+1

âˆ´p(âˆ’1/3)=3(âˆ’1/3)+1=âˆ’1+1=0Â

âˆ´âˆ’1/3Â is a zero of p(x).

**(ii) p(x)=5xâ€“Ï€, x=4/5**

Solution:

For,Â x=4/5Â p(x)=5xâ€“Ï€

âˆ´p(4/5)=5(4/5)â€“Ï€=4âˆ’Ï€Â

âˆ´Â 4/5is not a zero of p(x).

**(iii) p(x)=x ^{2}âˆ’1, x=1, âˆ’1**

Solution:

For,Â x=1, âˆ’1;Â

p(x)=x^{2}âˆ’1

âˆ´p(1)=1^{2}âˆ’1=1âˆ’1=0

p(âˆ’1)=(-1)^{2}âˆ’1=1âˆ’1=0

âˆ´1, âˆ’1Â are zeros of p(x).

**(iv) p(x)=(x+1)(xâ€“2), x= âˆ’1, 2**

Solution:

For,Â x=âˆ’1,2;Â

p(x)=(x+1)(xâ€“2)

âˆ´p(âˆ’1)=(âˆ’1+1)(âˆ’1â€“2)

=((0)(âˆ’3))=0

p(2)=(2+1)(2â€“2)=(3)(0)=0Â

âˆ´âˆ’1,2Â are zeros of p(x).

**(v) p(x)=x ^{2}, x=0**

Solution:

For,Â x=0Â p(x)= x^{2}

p(0)=0^{2}=0Â

âˆ´0Â is aÂ zero of p(x).

**(vi) p(x)=lx+m, x=âˆ’m/t**

Solution:

For,Â x=âˆ’m/t; Â p(x)=lx+m

âˆ´p(âˆ’m/t)=l(âˆ’m/t)+m=âˆ’m+m=0Â

âˆ´âˆ’m/tis a zero of p(x).

**(vii) p(x)=3x ^{2}âˆ’1,x=âˆ’1/âˆš3,2/âˆš3,**

Solution:

For,Â x=âˆ’1/âˆš3,2/âˆš3,; p(x)=3x^{2}âˆ’1

âˆ´p(âˆ’1/âˆš3)=3(âˆ’1/âˆš3)^{2}âˆ’1=3(1/âˆš3)âˆ’1=1âˆ’1=0

âˆ´p(2/âˆš3)=3(2/âˆš3)^{2}âˆ’1=3(4/3)âˆ’1=4âˆ’1=3â‰ 0Â

âˆ´âˆ’âˆ’1/âˆš3Â is a zero of p(x) butÂ 2/âˆš3Â is not a zero of p(x).

**(viii) p(x)=2x+1,x=1/2**

Solution:

For,Â x=1/2Â p(x)=2x+1

âˆ´p(1/2)=2(1/2)+1=1+1=2â‰ 0Â

âˆ´Â 1/2 is not aÂ zero of p(x).

Â

## Exercise 2.2 Page: 35

**Q4. Find the zero of the polynomial in each of the following cases:****(i) p(x) =Â xÂ + 5Â **

Solution:

p(x)=x+5

â‡’x+5=0

â‡’x=âˆ’5Â

âˆ´-5 is a zero polynomial of the polynomial p(x).

**(ii) p(x) =Â xÂ â€“ 5**

Solution:

p(x)=xâˆ’5

â‡’xâˆ’5=0

â‡’x=5Â

âˆ´5 is a zero polynomial of the polynomial p(x).

**(iii) p(x) = 2xÂ + 5**

Solution:

p(x)=2x+5

â‡’2x+5=0

â‡’2x=âˆ’5

â‡’x=âˆ’5/2Â

âˆ´x= âˆ’5/2 Â is a zero polynomial of the polynomial p(x).

**(iv) p(x) = 3xÂ â€“ 2Â **

Solution:

p(x)=3xâ€“2

â‡’3xâˆ’2=0

â‡’3x=2

â‡’x=2/3Â

âˆ´x=2/3Â is a zero polynomial of the polynomial p(x).

**(v) p(x) = 3xÂ **

Solution:

p(x)=3x

â‡’3x=0

â‡’x=0Â

âˆ´0 is a zero polynomial of the polynomial p(x).

**(vi) p(x) = ax, a0**

Solution:

p(x)=ax

â‡’ax=0

â‡’x=0

âˆ´x=0 is a zero polynomial of the polynomial p(x).

**(vii) p(x) = cx + d, c â‰ 0, c, d are real numbers.**

Solution:

p(x)= cx + d

â‡’ cx + d =0

â‡’x=-d/cÂ

âˆ´ x=-d/cÂ is a zero polynomial of the polynomial p(x).

Â

## Exercise 2.3 Page: 40

Â **Q1. Find the remainder whenÂ x ^{3}+3x^{2}+3x+1Â is divided by**

**(i) x+1**

Solution:

x+1=0

â‡’x=âˆ’1Â

âˆ´Remainder:

p(âˆ’1)=(âˆ’1)^{3}+3(âˆ’1)^{2}+3(âˆ’1)+1

=âˆ’1+3âˆ’3+1

=0

**(ii) xâˆ’1/2**

Solution:

xâˆ’1/2=0

â‡’x=Â 1/2

âˆ´Remainder:

p(1/2 )= (1/2)^{3}+3(1/2)^{2}+3()+1

=1/8+3/4+3/2+1

=27/8

**(iii) x**

Solution:

x=0

âˆ´Remainder:

p(0)=(0)^{3}+3(0)^{2}+3(0)+1

=1

**(iv) x+Ï€**

Solution:

x+Ï€=0

â‡’x=âˆ’Ï€Â

âˆ´Remainder:

p(0)=(âˆ’Ï€)^{3}+3(âˆ’Ï€)^{2}+3(âˆ’Ï€)+1

=âˆ’Ï€^{3}+3Ï€^{2}âˆ’3Ï€+1

**(v) 5+2x**

Solution:

5+2x=0

â‡’2x=âˆ’5

â‡’x=âˆ’Â 5/2

âˆ´Remainder:

(âˆ’5/2)^{3}+3(âˆ’5/2)^{2}+3(âˆ’5/2)+1=âˆ’125/8+75/4âˆ’15/2+1

=âˆ’27/8

Â **Q2. Find the remainder whenÂ x ^{3}âˆ’ax^{2}+6xâˆ’aÂ is divided by x-a.**

Solution:

LetÂ p(x)=x^{3}âˆ’ax^{2}+6xâˆ’a

xâˆ’a=0Â

âˆ´x=aÂ

Remainder:

p(a)= (a)^{3} âˆ’a(a^{2})+6(a)âˆ’a

=a^{3}âˆ’a^{3}+6aâˆ’a = 5a

Â **Q3. Check whether 7+3x is a factor ofÂ 3x ^{3}+7x.**

Solution:

7+3x=0

â‡’3x=âˆ’7Â only if 7+3x dividesÂ 3x^{3}+7x leaving no remainder.

â‡’x=-7/3Â

âˆ´Remainder:

3(7/3)^{3}+7(7/3)= âˆ’343/9+(-49/3)

= âˆ’343+(-49)3/9

= -343-147/9

= -490/9â‰ 0Â

âˆ´7+3x is not a factor ofÂ 3x^{3}+7x

Â

## Exercise 2.4 Page: 43

Â **Q1. Determine which of the following polynomials has (xÂ + 1) a factor:**

**(i) x ^{3}+x^{2}+x+1**

Solution:

Let p(x)=Â x^{3}+x^{2}+x+1

The zero of x+1 is -1. [x+1=0 means x=-1]

p(âˆ’1)=(âˆ’1)^{3}+(âˆ’1)^{2}+(âˆ’1)+1

=âˆ’1+1âˆ’1+1

=0Â

âˆ´By factor theorem, x+1 is a factor ofÂ x^{3}+x^{2}+x+1

**(ii) x ^{4}Â +Â x^{3}Â +Â x^{2}Â +Â xÂ + 1**

Solution:

Let p(x)=Â x^{4}Â +Â x^{3}Â +Â x^{2}Â +Â xÂ + 1

The zero of x+1 is -1. . [x+1=0 means x=-1]

p(âˆ’1)=(âˆ’1)^{4}+(âˆ’1)^{3}+(âˆ’1)^{2}+(âˆ’1)+1

=1âˆ’1+1âˆ’1+1

=1â‰ 0Â

âˆ´By factor theorem, x+1 is a factor ofÂ x^{4}Â +Â x^{3}Â +Â x^{2}Â +Â xÂ + 1

**(iii) x ^{4}Â + 3x^{3}Â + 3x^{2}Â +Â xÂ + 1Â **

Solution:

Let p(x)=Â x^{4}Â + 3x^{3}Â + 3x^{2}Â +Â xÂ + 1Â

The zero of x+1 is -1.

p(âˆ’1)=(âˆ’1)4+3(âˆ’1)3+3(âˆ’1)2+(âˆ’1)+1

=1âˆ’3+3âˆ’1+1

=1â‰ 0Â

âˆ´By factor theorem, x+1 is a factor of x^{4} + 3x^{3} + 3x^{2} + x + 1

**(iv) x ^{3} â€“ x^{2} â€“ (2 +âˆš2 )x +âˆš2 **

Solution:

Let p(x)=Â x^{3} â€“ x^{2} â€“ (2 + âˆš2)x +âˆš2

The zero of x+1 is -1.

p(âˆ’1)=(âˆ’1)^{3}â€“(âˆ’1)^{2}â€“(2+âˆš2)(âˆ’1)+âˆš2

=âˆ’1âˆ’1+2+âˆš2+âˆš2

= 2âˆš2

âˆ´By factor theorem, x+1 is not a factor ofÂ x^{3} â€“ x^{2} â€“ (2 +âˆš2 )x +âˆš2

Â

## Exercise 2.4 Page: 44

**Q2. Use the Factor Theorem to determine whetherÂ g(x) is a factor ofÂ p(x) in each of the following cases:****(i) p(x)=2x ^{3}+x^{2}â€“2xâ€“1,Â g(x) =Â xÂ + 1**

Solution:

p(x)= 2x^{3}+x^{2}â€“2xâ€“1,Â g(x) =Â xÂ + 1

g(x)=0

â‡’x+1=0

â‡’x=âˆ’1Â

âˆ´Zero of g(x) is -1.

Now,Â

p(âˆ’1)=2(âˆ’1)^{3}+(âˆ’1)^{2}â€“2(âˆ’1)â€“1

=âˆ’2+1+2âˆ’1

=0Â

âˆ´By factor theorem, g(x) is a factor of p(x).

**(ii) p(x)=x ^{3}+3x^{2}+3x+1,Â g(x) =Â xÂ + 2**

Solution:

p(x)=x3+3Ã—2+3x+1,Â g(x) =Â xÂ + 2

g(x)=0

â‡’x+2=0

â‡’x=âˆ’2Â

âˆ´Zero of g(x) is -2.

Now,Â

p(âˆ’2)=(âˆ’2)^{3}+3(âˆ’2)^{2}+3(âˆ’2)+1

=âˆ’8+12âˆ’6+1

=âˆ’1â‰ 0Â

âˆ´By factor theorem, g(x) is not a factor of p(x).

**(iii) p(x)=x ^{3}â€“4x^{2}+x+6,Â g(x) =Â xÂ â€“ 3**

Solution:

p(x)= x^{3}â€“4x^{2}+x+6,Â g(x) =Â xÂ -3

g(x)=0

â‡’xâˆ’3=0

â‡’x=3Â

âˆ´Zero of g(x) is 3.

Now,

p(3)=(3)^{3}âˆ’4(3)^{2}+(3)+6

=27âˆ’36+3+6

=0Â

âˆ´By factor theorem, g(x) is a factor of p(x).

Â **Q3. Find the value ofÂ k, ifÂ xÂ â€“ 1 is a factor ofÂ p(x) in each of the following cases:****(i) p(x)=x ^{2}+x+k**

Solution:

If x-1 is a factor of p(x), then p(1)=0Â Â

By Factor TheoremÂ

â‡’(1)^{2}+(1)+k=0

â‡’1+1+k=0Â

â‡’2+k=0

â‡’k=âˆ’2

**(ii) p(x)=2x ^{2}+kx+âˆš2**

Solution:

If x-1 is a factor of p(x), then p(1)=0

â‡’2(1)^{2}+k(1)+âˆš2 =0

â‡’2+k+âˆš2=0

â‡’k = âˆ’(2+âˆš2)

**(iii) p(x)=kx ^{2}â€“âˆš2x+1**

Solution:

If x-1 is a factor of p(x), then p(1)=0

By Factor Theorem

â‡’k(1)^{2}âˆ’âˆš2(1)+1=0

â‡’k = âˆš2âˆ’1Â

**(iv) p(x)=kx ^{2}â€“3x+k**

Solution:

If x-1 is a factor of p(x), then p(1)=0

By Factor Theorem

â‡’k(1)^{2}â€“3(1)+k=0

â‡’kâˆ’3+k=0

â‡’2kâˆ’3=0

â‡’k=

Â **Q4. Factorize:**

**(i) 12x ^{2}â€“7x+1**

Solution:

Using the splitting the middle term method,

We have to find a number whose sum=-7 and product=112=12

We get -3 and -4 as the numbers [-3+-4=-7 and -3-4=12]

12x^{2}â€“7x+1=12x^{2}-4x-3x+1

=4x (3x-1)-1(3x-1)

= (4x-1)(3x-1)

**(ii) 2x ^{2}+7x+3**

Solution:

Using the splitting the middle term method,

We have to find a number whose sum=7 and product=2=6

We get 6 and 1 as the numbers [6+1=7 and 6=6]

2x^{2}+7x+3 =2x^{2}+6x+1x+3

=2x (x+3)+1(x+3)

= (2x+1)(x+3)

**(iii) 6x ^{2}+5x-6Â **

Solution:

Using the splitting the middle term method,

We have to find a number whose sum=5 and product=6= -36

We get -4 and 9 as the numbers [-4+9=5 and -4=-36]

6x^{2}+5x-6=6x^{2}+ 9x â€“ 4x â€“ 6

=3x (2x + 3) â€“ 2 (2x + 3)

= (2x + 3) (3x â€“ 2)

**(iv) 3x ^{2}Â â€“Â xÂ â€“ 4Â **

Solution:

Using the splitting the middle term method,

We have to find a number whose sum=-1 and product=3= -12

We get -4 and 3 as the numbers [-4+3=-1 and -4=-12]

3x^{2}Â â€“Â xÂ â€“ 4 =3x^{2}â€“xâ€“4

=3x^{2}â€“4x+3xâ€“4

=x(3xâ€“4)+1(3xâ€“4)

=(3xâ€“4)(x+1)

Â **Q5. Factorize:****x ^{3}â€“2x^{2}â€“x+2**

Solution:

LetÂ p(x)=x^{3}â€“2x^{2}â€“x+2Â

Factors of 2 are Â±1 and Â± 2

By trial method, we find that

p(1)Â = 0

So,Â (x+1)Â is factor ofÂ p(x)

Now,

p(x)= x^{3}â€“2x^{2}â€“x+2

p(âˆ’1)=(âˆ’1)^{3}â€“2(âˆ’1)^{2}â€“(âˆ’1)+2

=âˆ’1âˆ’1+1+2

=0

Therefore, (x+1) is the factor ofÂ Â p(x)

Now, Dividend = Divisor Ã— QuotientÂ + Remainder

(x+1)(x^{2}â€“3x+2) =(x+1)(x^{2}â€“xâ€“2x+2)

=(x+1)(x(xâˆ’1)âˆ’2(xâˆ’1))

=(x+1)(xâˆ’1)(x+2)

**(ii) x ^{3}â€“3x^{2}â€“9xâ€“5**

Solution:

LetÂ p(x) =Â x^{3}â€“3x^{2}â€“9xâ€“5Â

Factors of 5 are Â±1 and Â±5

By trial method, we find that

p(5)Â = 0

So,Â (x-5)Â is factor ofÂ p(x)

Now,

p(x) =Â x^{3}â€“3x^{2}â€“9xâ€“5

p(5) =Â (5)^{3}â€“3(5)^{2}â€“9(5)â€“5

=125âˆ’75âˆ’45âˆ’5

=0

Therefore, (x-5) is the factor ofÂ Â p(x)

Now, Dividend = Divisor Ã— QuotientÂ + Remainder

(xâˆ’5)(x^{2}+2x+1) =(xâˆ’5)(x^{2}+x+x+1)

=(xâˆ’5)(x(x+1)+1(x+1))

=(xâˆ’5)(x+1)(x+1)

**(iii) x ^{3}+13x^{2}+32x+20**

Solution:

LetÂ p(x) =Â x^{3}+13x^{2}+32x+20

Factors of 20 are Â±1, Â±2, Â±4, Â±5, Â±10 and Â±20

By trial method, we find that

p(-1)Â = 0

So,Â (x+1)Â is factor ofÂ p(x)

Now,

p(x) =Â x^{3}+13x^{2}+32x+20

p(-1) =Â (âˆ’1)^{3}+13(âˆ’1)^{2}+32(âˆ’1)+20

=âˆ’1+13âˆ’32+20

=0

Therefore, (x+1) is the factor ofÂ Â p(x)

Now, Dividend = Divisor Ã— QuotientÂ + Remainder

(x+1)(x^{2}+12x+20) =(x+1)(x^{2}+2x+10x+20)

=(xâˆ’5)x(x+2)+10(x+2)

=(xâˆ’5)(x+2)(x+10)

**(iv) 2y ^{3}+y^{2}â€“2yâ€“1**

Solution:

LetÂ p(y) =Â 2y^{3}+y^{2}â€“2yâ€“1

Factors =Â 2Ã—(âˆ’1)= -2 are Â±1 and Â±2

By trial method, we find that

p(1)Â = 0

So,Â (y-1)Â is factor ofÂ p(y)

Now,

p(y) =Â 2y^{3}+y^{2}â€“2yâ€“1

p(1) =Â 2(1)^{3}+(1)^{2}â€“2(1)â€“1

=2+1âˆ’2

=0

Therefore, (y-1) is the factor ofÂ Â p(y)

Now, Dividend = Divisor Ã— QuotientÂ + Remainder

(yâˆ’1)(2y^{2}+3y+1) =(yâˆ’1)(2y^{2}+2y+y+1)

=(yâˆ’1)(2y(y+1)+1(y+1))

=(yâˆ’1)(2y+1)(y+1)

Â

### Exercise 2.5 Page: 48

Â **Q1. Use suitable identities to find the following products:****(i) (xÂ + 4) (xÂ + 10)Â **

Solution:

Using the identity, (x + a) (x + b) = x ^{2} + (a + b)x + ab

We get,

(x+4)(x+10) =x^{2}+(4+10)x+(4Ã—10)

=x^{2}+14x+40Â

**(ii) (xÂ + 8) (xÂ â€“ 10)Â Â Â Â Â **

Solution:

Using the identity, (x + a) (x + b) = x ^{2} + (a + b)x + ab

We get,

(x+8)(xâˆ’10) =x^{2}+(8+(âˆ’10))x+(8Ã—(âˆ’10))

=x^{2}+(8âˆ’10)xâ€“80

=x^{2}âˆ’2xâˆ’80

**(iii) (3xÂ + 4) (3xÂ â€“ 5)**

Solution:

Using the identity, (x + a) (x + b) = x ^{2} + (a + b)x + ab

We get,

(3x+4)(3xâˆ’5) =(3x)^{2}+4+(âˆ’5)3x+4Ã—(âˆ’5)

=9x^{2}+3x(4â€“5)â€“20

=9x^{2}â€“3xâ€“20Â

**(iv) (y ^{2}+3/2)(y^{2}â€“3/2 )**

Solution:

Using the identity, (x + y) (x â€“ y) = x ^{2} â€“ y^{ 2}

^{2}and y=3/2]

We get,

(y^{2}+3/2)(y^{2}â€“3/2) = (y^{2})^{2}â€“(3/2)^{2}

=y^{4}â€“(9/4)

Â **Q2. Evaluate the following products without multiplying directly:****(i) 103 Ã— 107**

Solution:

103Ã—107=(100+3)Ã—(100+7)

Exercise 2.5 Page: 48

Using identity, [(x+a)(x+b)=x2+(a+b)x+ab

Here, x=100

a=3

b=7

We get, 103Ã—107=(100+3)Ã—(100+7)

=(100)^{2}+(3+7)100+(3Ã—7))

=10000+1000+21

=11021

**(ii) 95 Ã— 96 Â **

Solution:

95Ã—96=(100-5)Ã—(100-4)

Using identity, [(x-a)(x-b)=x^{2}+(a+b)x+ab

Here, x=100

a=-5

b=-4

We get, 95Ã—96=(100-5)Ã—(100-4)

=(100)^{2}+100(-5+(-4))+(-5Ã—-4)

=10000-900+20

=9120

**(iii) 104 Ã— 96**

Solution:

104Ã—96=(100+4)Ã—(100â€“4)

Using identity, [(a+b)(a-b)= a^{2}-b^{2}]

Here, a=100

b=4

We get, 104Ã—96=(100+4)Ã—(100â€“4)

=(100)^{2}â€“(4)^{2}

=10000â€“16

=9984

Â

### Exercise 2.5 Page: 48

**Q3. Factorize the following using appropriate identities:****(i) 9x ^{2}+6xy+y^{2}**

Solution:

9x^{2}+6xy+y^{2}=(3x)^{2}+(2Ã—3xÃ—y)+y^{2}

Using identity, x^{2} + 2xy + y^{2}= (x + y)^{2}

Here, x=3x

y=y

9x^{2}+6xy+y^{2}=(3x)^{2}+(2Ã—3xÃ—y)+y^{2}

=(3x+y)^{2}

=(3x+y)(3x+y)

**(ii) 4y ^{2}âˆ’4y+1**

Solution:

4y^{2}âˆ’4y+1=(2y)^{2}â€“(2Ã—2yÃ—1)+12

Using identity, x^{2} â€“ 2xy + y^{2}= (x â€“ y)^{2}

Here, x=2y

y=1

4y^{2}âˆ’4y+1=(2y)^{2}â€“(2Ã—2yÃ—1)+1^{2}

=(2yâ€“1)^{2}

=(2yâ€“1)(2yâ€“1)

**(iii)Â x ^{2}â€“y^{2/100}**

Solution:

x^{2}â€“y^{2/100 = x2â€“(y/10)2}

Using identity, x^{2} â€“ y^{2}= (x â€“ y) (x y)

Here,

x=x

y=y/10

x^{2 }â€“ y^{2}/100= x^{2}â€“(y/10)^{2}

=(xâ€“y/10)(x+y/10)

Â **Q4. Expand each of the following, using suitable identities:****(i) (x+2y+4z) ^{2}**

**(ii) (2xâˆ’y+z)**

^{2}**(iii) (âˆ’2x+3y+2z)**

^{2}**(iv) (3a â€“ 7b â€“ c)**

^{2}**(v) (â€“2x + 5y â€“ 3z)**

^{2}**(vi) (aâ€“b+1)**

^{2}Solutions:

**(i) (x+2y+4z) ^{2}**

Solution:

Using identity, (x + y + z)^{2} = x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx

Here, x=x

y=2y

z=4z

(x+2y+4z)^{2 }=x^{2}+(2y)^{2}+(4z)^{2}+(2Ã—xÃ—2y)+(2Ã—2yÃ—4z)+(2Ã—4zÃ—x)

=x^{2}+4y^{2}+16z^{2}+4xy+16yz+8xz

**(ii) (2xâˆ’y+z) ^{2}Â **

Solution:

Using identity, (x + y + z)^{2} = x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx

Here, x=2x

y=âˆ’y

z=z

(2xâˆ’y+z)^{2 }=(2x)^{2}+(âˆ’y)^{2}+z^{2}+(2Ã—2xÃ—âˆ’y)+(2Ã—âˆ’yÃ—z)+(2Ã—zÃ—2x)

=4x^{2}+y^{2}+z^{2}â€“4xyâ€“2yz+4xz

**(iii) (âˆ’2x+3y+2z) ^{2}**

Solution:

Using identity, (x + y + z)^{2} = x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx

Here, x= âˆ’2x

y=3y

z=2z

(âˆ’2x+3y+2z)^{2 }=(âˆ’2x)^{2}+(3y)^{2}+(2z)^{2}+(2Ã—âˆ’2xÃ—3y)+(2Ã—3yÃ—2z)+(2Ã—2zÃ—âˆ’2x)

=4x^{2}+9y^{2}+4z^{2}â€“12xy+12yzâ€“8xzÂ

**(iv) (3a â€“ 7b â€“ c) ^{2}**

Solution:

Using identity, (x + y + z)^{2} = x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx

Here, x= 3a

y= â€“ 7b

z= â€“ c

(3a â€“ 7b â€“ c)^{2 }=(3a)^{2}+(â€“ 7b)^{2}+(â€“ c)^{2}+(2Ã—3a Ã—â€“ 7b)+(2Ã—â€“ 7b Ã—â€“ c)+(2Ã—â€“ c Ã—3a)

=9a^{2} + 49b^{2 }+ c^{2}â€“ 42ab+14bcâ€“6ca

**(v) (â€“2x + 5y â€“ 3z) ^{2}**

Solution:

Using identity, (x + y + z)^{2} = x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx

Here, x= â€“2x

y= 5y

z= â€“ 3z

(â€“2x+5yâ€“3z)^{2 }=(â€“2x)^{2}+(5y)^{2}+(â€“3z)^{2}+(2Ã—â€“2x Ã— 5y)+(2Ã— 5y Ã—â€“ 3z)+(2Ã—â€“3z Ã—â€“2x)

=4x^{2} + 25y^{2 }+ 9z^{2}â€“ 20xyâ€“30yz+12zx

**(vi) (1/4a â€“ 1/2b+1) ^{2}**

Solution:

Using identity, (x + y + z)^{2} = x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx

Here, x= 1/4a

y= â€“1/2b

z= 1

(1/4a â€“1/2b +1)^{2 }=(1/4a)^{2}+(â€“1/2b)^{2}+(1)^{2}+(2Ã—1/4a Ã— â€“1/2b)+(2Ã— â€“1/2b Ã—1)+(2Ã—1Ã—1/4a)

=1/16a^{2}+1/4b^{2}+1^{2}â€“2/8abâ€“ 2/2b +2/4a

= 1/16a^{2}+1/4b^{2}+1â€“1/4ab â€“ b +1/2a

Â **Q5. Factorize:**

**(i) 4x ^{2}+9y^{2}+16z^{2}+12xyâ€“24yzâ€“16xz**

**(ii) 2x**

^{2}+y^{2}+8z^{2}â€“2xy+4yzâ€“8xzSolutions:

**(i) 4x ^{2}+9y^{2}+16z^{2}+12xyâ€“24yzâ€“16xz**

Solution:

Using identity, (x + y + z)^{2} = x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx

We can say that, x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx = (x + y + z)^{2}

4x^{2}+9y^{2}+16z^{2}+12xyâ€“24yzâ€“16xzÂ =(2x)^{2}+(3y)^{2}+(âˆ’4z)^{2}+(2Ã—2xÃ—3y)+(2Ã—3yÃ—âˆ’4z)+(2Ã—âˆ’4zÃ—2x)

=(2x+3yâ€“4z)^{2}

=(2x+3yâ€“4z)(2x+3yâ€“4z)

**(ii) 2x ^{2}+y^{2}+8z^{2}â€“2âˆš2xy+4âˆš2yzâ€“8xz**

Solution:

Using identity, (x + y + z)^{2} = x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx

We can say that, x^{2} + y^{2} + z^{2} + 2xy + 2yz + 2zx = (x + y + z)^{2}

2x^{2}+y^{2}+8z^{2}â€“2âˆš2xy+4âˆš2yzâ€“8xzÂ =(-âˆš2x)^{2}+(y)^{2}+(2âˆš2z)^{2}+(2Ã—âˆ’âˆš2xÃ—y)+(2Ã—yÃ—2âˆš2z)+(2Ã—2âˆš2âˆš2zÃ—âˆ’âˆš2x)

=(âˆ’âˆš2x+y+2âˆš2z)^{2}

=(âˆ’âˆš2x+y+2âˆš2z)(âˆ’âˆš2x+y+2âˆš2z)

Â **Q6. Write the following cubes in expanded form:****(i) (2x+1) ^{3}**

**(ii) (2aâˆ’3b)**

^{3}**(iii) (x+1)**

^{3}**(iv) (xâˆ’y)**

^{3}Solutions:

**(i) (2x+1) ^{3}**

Solution:

Using identity, (x + y)^{3} = x^{3} + y^{3} + 3xy (x + y)

(2x+1)^{3}=(2x)^{3}+1^{3}+(3Ã—2xÃ—1)(2x+1)

=8x^{3}+1+6x(2x+1)

=8x^{3}+12x^{2}+6x+1

**(ii) (2aâˆ’3b) ^{3}**

Solution:

Using identity, (x â€“ y)^{3} = x^{3} â€“ y^{3} â€“ 3xy(x â€“ y)

(2aâˆ’3b)^{3}=(2a)^{3}âˆ’(3b)^{3}â€“(3Ã—2aÃ—3b)(2aâ€“3b)

=8a^{3}â€“27b^{3}â€“18ab(2aâ€“3b)

=8a^{3}â€“27b^{3}â€“36a^{2}b+54ab^{2}

**(iii) (3/2x+1) ^{3}**

Solution:

Using identity, (x + y)^{3} = x^{3} + y^{3} + 3xy (x + y)

(3/2x+1)^{3 }=(3/2x)^{3}+1^{3}+(3Ã—3/2xÃ—1)(3/2x+1)

=27/8x^{3}+1+9/2x(3/2x+1)

=27/8x^{3}+1+27/4x^{2}+9/2x

=27/8x^{3}+27/4x^{2}+9/2x+1

**(iv)Â (xâˆ’2/3y) ^{3}**

Solution:

Using identity, (x â€“ y)^{3} = x^{3} â€“ y^{3} â€“ 3xy(x â€“ y)

(xâˆ’2/3y)^{3 }=(x)^{3}â€“(2/3y)^{3}â€“(3Ã—xÃ—2/3y)(xâ€“2/3y)

=(x)^{3}â€“8/27y^{3}â€“2xy(xâ€“ 2/3y)

=(x)^{3}â€“8/27y^{3}â€“2x^{2}y+4/3xy^{2}

Â **Q7. Evaluate the following using suitable identities:Â ****(i) (99) ^{3}**

**(ii) (102)**

^{3}**(iii) (998)**

^{3}Solutions:

**(i) (99) ^{3}**

Solution:

We can write 99 as 100â€“1

Using identity, (x â€“ y)^{3} = x^{3} â€“ y^{3} â€“ 3xy(x â€“ y)

(99)^{3 }= (100â€“1)^{3}

=(100)^{3}â€“1^{3}â€“(3Ã—100Ã—1)(100â€“1)

= 1000000 â€“ 1 â€“ 300(100 â€“ 1)

= 1000000 â€“ 1 â€“ 30000 + 300

= 970299

**(ii) (102) ^{3}**

Solution:

We can write 102 as 100+2

Using identity, (x + y)^{3} = x^{3} + y^{3} + 3xy (x + y)

(100+2)^{3 }=(100)^{3}+2^{3}+(3Ã—100Ã—2)(100+2)Â

= 1000000 + 8 + 600(100 + 2)

= 1000000 + 8 + 60000 + 1200

= 1061208

**(iii) (998) ^{3}**

Solution:

We can write 99 as 1000â€“2

Using identity, (x â€“ y)^{3} = x^{3} â€“ y^{3} â€“ 3xy(x â€“ y)

(998)^{3 }=(1000â€“2)^{3}

=(1000)^{3}â€“2^{3}â€“(3Ã—1000Ã—2)(1000â€“2)

= 1000000000 â€“ 8 â€“ 6000(1000 â€“ 2)

= 1000000000 â€“ 8- 6000000 + 12000

= 994011992

Â

Â Exercise 2.5 Page: 49

**Q8. Factorise each of the following:****(i) 8a ^{3}+b^{3}+12a^{2}b+6ab^{2}**

**(ii) 8a**

^{3}â€“b^{3}â€“12a^{2}b+6ab^{2}**(iii) 27 â€“ 125a**

^{3}Â â€“ 135a + 225a^{2}Â Â**(iv) 64a**

^{3}â€“27b^{3}â€“144a^{2}b+108ab^{2}**(v) 27p**

^{3}â€“1/216 âˆ’9/2p^{2}+1/4pSolutions:

**(i) 8a ^{3}+b^{3}+12a^{2}b+6ab^{2}**

Solution:

The expression, 8a^{3}+b^{3}+12a^{2}b+6ab^{2} can be written as (2a)^{3}+b^{3}+3(2a)^{2}b+3(2a)(b)^{2}

8a^{3}+b^{3}+12a^{2}b+6ab^{2 }=(2a)^{3}+b^{3}+3(2a)^{2}b+3(2a)(b)^{2}

=(2a+b)^{3}

=(2a+b)(2a+b)(2a+b)

Here, the identity, (x + y)^{3} = x^{3} + y^{3} + 3xy (x + y) is used.

**(ii) 8a ^{3}â€“b^{3}â€“12a^{2}b+6ab^{2}**

Solution:

The expression, 8a^{3}â€“b^{3}âˆ’12a^{2}b+6ab^{2} can be written as (2a)^{3}â€“b^{3}â€“3(2a)^{2}b+3(2a)(b)^{2}

8a^{3}â€“b^{3}âˆ’12a^{2}b+6ab^{2 }=(2a)^{3}â€“b^{3}â€“3(2a)^{2}b+3(2a)(b)^{2}

=(2aâ€“b)^{3}

=(2aâ€“b)(2aâ€“b)(2aâ€“b)

Here, the identity, (x â€“ y)^{3} = x^{3} â€“ y^{3} â€“ 3xy(x â€“ y) is used.

**(iii) 27 â€“ 125a ^{3}Â â€“ 135a + 225a^{2}Â **

Solution:

The expression, 27 â€“ 125a^{3}Â â€“ 135a + 225a^{2} can be written as 3^{3}â€“(5a)^{3}â€“3(3)^{2}(5a)+3(3)(5a)^{2}

27â€“125a^{3}â€“135a+225a^{2} = 3^{3}â€“(5a)^{3}â€“3(3)^{2}(5a)+3(3)(5a)^{2}

=(3â€“5a)^{3}

=(3â€“5a)(3â€“5a)(3â€“5a)

Â Here, the identity, (x â€“ y)^{3} = x^{3} â€“ y^{3} â€“ 3xy(x â€“ y) is used.

**(iv) 64a3â€“27b3â€“144a ^{2}b+108ab^{2}**

Solution:

The expression, 64a^{3}â€“27b^{3}â€“144a^{2}b+108ab^{2} can be written as (4a)^{3}â€“(3b)^{3}â€“3(4a)^{2}(3b)+3(4a)(3b)^{2}

64a^{3}â€“27b^{3}â€“144a^{2}b+108ab^{2} = (4a)^{3}â€“(3b)^{3}â€“3(4a)^{2}(3b)+3(4a)(3b)^{2}

=(4aâ€“3b)^{3}

=(4aâ€“3b)(4aâ€“3b)(4aâ€“3b)

Â Here, the identity, (x â€“ y)^{3} = x^{3} â€“ y^{3} â€“ 3xy(x â€“ y) is used.

**(v) 27p ^{3} â€“ 1/216 âˆ’ 9/2p^{2}+ 1/4p**

Solution:

The expression, 27p^{3} â€“1/216 âˆ’ 9/2p^{2}+ 1/4p can be written as (3p)^{3}â€“(1/6)^{3}â€“3(3p)^{2}(1/6)+3(3p)(1/6)^{2}

27p^{3} â€“ 1/216 âˆ’ 9/2p^{2}+ 1/4p = (3p)^{3}â€“(1/6)^{3}â€“3(3p)^{2}(1/6)+3(3p)(1/6)^{2}

= (3pâ€“16)^{3}

= (3pâ€“16)(3pâ€“16)(3pâ€“16)

Â

**Q9. Verify:****(i) x ^{3}+y^{3}=(x+y)(x^{2}â€“xy+y^{2})**

**(ii) x**

^{3}â€“y^{3}=(xâ€“y)(x^{2}+xy+y^{2})ÂSolutions:

(i) x^{3}+y^{3}=(x+y)(x^{2}â€“xy+y^{2})

We know that, (x+y)^{3} =x^{3}+y^{3}+3xy(x+y)

â‡’x^{3}+y^{3}=(x+y)^{3}â€“3xy(x+y)

â‡’x^{3}+y^{3}=(x+y)[(x+y)^{2}â€“3xy]

Taking(x+y) common â‡’x^{3}+y^{3}=(x+y)[(x^{2}+y^{2}+2xy)â€“3xy]

â‡’x^{3}+y^{3}=(x+y)(x^{2}+y^{2}â€“xy)

(ii) x^{3}â€“y^{3}=(xâ€“y)(x^{2}+xy+y^{2})Â

We know that,(xâ€“y)^{3} =x^{3}â€“y^{3}â€“3xy(xâ€“y)

â‡’x^{3}âˆ’y^{3}=(xâ€“y)^{3}+3xy(xâ€“y)

â‡’x^{3}âˆ’y^{3}=(xâ€“y)[(xâ€“y)^{2}+3xy]

Taking(x+y) commonâ‡’x^{3}âˆ’y^{3}=(xâ€“y)[(x^{2}+y^{2}â€“2xy)+3xy]

â‡’x^{3}+y^{3}=(xâ€“y)(x^{2}+y^{2}+xy)

Â **Q10. Factorize each of the following:****(i) 27y ^{3}+125z^{3}**

**(ii) 64m**

^{3}â€“343n^{3}Solutions:

(i) 27y^{3}+125z^{3}

The expression, 27y^{3}+125z^{3 }can be written as (3y)^{3}+(5z)^{3}

27y^{3}+125z^{3 }=(3y)^{3}+(5z)^{3}

We know that, x^{3}+y^{3}=(x+y)(x^{2}â€“xy+y^{2})

27y^{3}+125z^{3 }=(3y)^{3}+(5z)^{3}

=(3y+5z)[(3y)^{2}â€“(3y)(5z)+(5z)^{2}]

=(3y+5z)(9y^{2}â€“15yz+25z^{2})

(ii) 64m^{3}â€“343n^{3}

The expression, 64m^{3}â€“343n^{3 }can be written as (4m)^{3}â€“(7n)^{3}

64m^{3}â€“343n^{3 } = (4m)^{3}â€“(7n)^{3}

We know that, x^{3}â€“y^{3}=(xâ€“y)(x^{2}+xy+y^{2})Â

64m^{3}â€“343n^{3 }=(4m)^{3}â€“(7n)^{3}

=(4m+7n)[(4m)^{2}+(4m)(7n)+(7n)^{2}]

=(4m+7n)(16m^{2}+28mn+49n^{2})

Â

**Q11. Factorise :Â 27x ^{3}+y^{3}+z^{3}â€“9xyzÂ **

Solution:

The expression 27x^{3}+y^{3}+z^{3}â€“9xyzÂ can be written as (3x)^{3}+y^{3}+z^{3}â€“3(3x)(y)(z)

27x^{3}+y^{3}+z^{3}â€“9xyzÂ =(3x)^{3}+y^{3}+z^{3}â€“3(3x)(y)(z)

We know that, x^{3} + y^{3} + z^{3} â€“ 3xyz = (x + y + z)(x^{2} + y^{2} + z^{2} â€“ xy â€“ yz â€“ zx)

27x^{3}+y^{3}+z^{3}â€“9xyzÂ =(3x)^{3}+y^{3}+z^{3}â€“3(3x)(y)(z)

=(3x+y+z)(3x)^{2}+y^{2}+z^{2}â€“3xyâ€“yzâ€“3xz

=(3x+y+z)(9x^{2}+y^{2}+z^{2}â€“3xyâ€“yzâ€“3xz)

Â **Q12. Verify that:**

**x ^{3}+y^{3}+z^{3}â€“3xyz=(x+y+z)[(xâ€“y)^{2}+(yâ€“z)^{2}+(zâ€“x)^{2}]**

Solution:

We know that,

x^{3}+y^{3}+z^{3}âˆ’3xyz=(x+y+z)(x^{2}+y^{2}+z^{2}â€“xyâ€“yzâ€“xz)

â‡’x^{3}+y^{3}+z^{3}â€“3xyz =Ã—(x+y+z)[2(x^{2}+y^{2}+z^{2}â€“xyâ€“yzâ€“xz)]

= (x+y+z)(2x^{2}+2y^{2}+2z^{2}â€“2xyâ€“2yzâ€“2xz)

= (x+y+z)[(x^{2}+y^{2}âˆ’2xy)+(y^{2}+z^{2}â€“2yz)+(x^{2}+z^{2}â€“2xz)]

= (x+y+z)[(xâ€“y)^{2}+(yâ€“z)^{2}+(zâ€“x)^{2}]

Â **Q13. IfÂ x + y + z =Â 0, show thatÂ x ^{3}+y^{3}+z^{3}=3xyz.**

Solution:

We know that,

x^{3}+y^{3}+z^{3}=3xyz = (x + y + z)(x^{2}Â +Â y^{2}Â +Â z^{2}Â â€“Â xy â€“ yz â€“ xz)

Now, according to the question, let (x + y + z) =Â 0,Â Â

then, x^{3}+y^{3}+z^{3}=3xyz =(0)(x^{2}+y^{2}+z^{2}â€“xyâ€“yzâ€“xz)

â‡’x^{3}+y^{3}+z^{3}â€“3xyz =0

Â â‡’ x^{3}+y^{3}+z^{3 }=3xyz

Hence Proved

Â **Q14. Without actually calculating the cubes, find the value of each of the following:****(i) (âˆ’12) ^{3}+(7)^{3}+(5)^{3}**

**(ii) (28)**

^{3}+(âˆ’15)^{3}+(âˆ’13)^{3}**(i) (âˆ’12) ^{3}+(7)^{3}+(5)^{3}**

Solution:

(âˆ’12)^{3}+(7)^{3}+(5)^{3}

Let a= âˆ’12

b= 7

c= 5

We know that ifÂ x + y + z =Â 0, then x^{3}+y^{3}+z^{3}=3xyz.

Here, âˆ’12+7+5=0

(âˆ’12)^{3}+(7)^{3}+(5)^{3 }= 3xyz

=

=

**(ii) (28) ^{3}+(âˆ’15)^{3}+(âˆ’13)^{3}**

Solution:

(28)^{3}+(âˆ’15)^{3}+(âˆ’13)^{3}

Let a= 28

b= âˆ’15

c= âˆ’13

We know that ifÂ x + y + z =Â 0, then x^{3}+y^{3}+z^{3}=3xyz.

Here, x + y + zÂ = 28 â€“ 15 â€“ 13 = 0

(28)^{3}+(âˆ’15)^{3}+(âˆ’13)^{3}= 3xyz

= 0+3(28)(âˆ’15)(âˆ’13)

=16380

Â **Q15. Give possible expressions for the length and breadth of each of the following rectangles, in which their areas are given:Â ****(i) Area :Â 25a ^{2}â€“35a+12**

**(ii) Area :Â 35y**

^{2}+13yâ€“12Solution:

(i) Area :Â 25a^{2}â€“35a+12

Using the splitting the middle term method,

We have to find a number whose sum= -35 and product=2512=300

We get -15 and -20 as the numbers [-15+-20=-35 and -3-4=300]

Â Â Exercise 2.5 Page: 50

25a^{2}â€“35a+12 =25a^{2}â€“15aâˆ’20a+12

=5a(5aâ€“3)â€“4(5aâ€“3)

=(5aâ€“4)(5aâ€“3)

Possible expression for lengthÂ = 5a â€“ 4

Possible expression for breadthÂ = 5a â€“ 3

(ii) Area :Â 35y^{2}+13yâ€“12

Using the splitting the middle term method,

We have to find a number whose sum= 13 and product=3512=420

We get -15 and 28 as the numbers [-15+28=-35 and -15=420]

35y^{2}+13yâ€“12 =35y^{2}â€“15y+28yâ€“12

=5y(7yâ€“3)+4(7yâ€“3)

=(5y+4)(7yâ€“3)

Possible expression for lengthÂ =Â (5yÂ + 4)

Possible expression for breadthÂ =Â (7y â€“ 3)

Â **Q16. What are the possible expressions for the dimensions of the cuboids whose volumes are given below?Â ****(i) Volume :Â 3x ^{2}â€“12x**

**(ii) Volume :Â 12ky**

^{2}+8kyâ€“20kSolution:

(i) Volume :Â 3x^{2}â€“12x

3x^{2}â€“12xÂ can be written as 3x(x â€“ 4) by taking 3x out of both the terms.

Possible expression for lengthÂ =Â 3

Possible expression for breadthÂ =Â x

Possible expression for heightÂ =Â (x â€“ 4)

(ii) Volume :Â 12ky^{2}+8ky â€“20kÂ

12ky^{2}+8ky â€“20kÂ can be written as 4k(3y^{2}+2yâ€“5) by taking 4k out of both the terms.

12ky^{2}+8kyâ€“20k =4k(3y^{2}+2yâ€“5)

^{2}+2yâ€“5 can be written as 3y

^{2}+5yâ€“3yâ€“5 using splitting the middle term method.]

=4k(3y^{2}+5yâ€“3yâ€“5)

=4k[y(3y+5)â€“1(3y+5)]

=4k(3y+5)(yâ€“1)

Possible expression for lengthÂ = 4k

Possible expression for breadthÂ =Â (3y +5)

Possible expression for heightÂ =Â (y -1)Â

## NCERT Solutions for class 9 Maths Chapter 2- Polynomials

As this is one of the important topics in maths, It comes under the unit â€“ Algebra which has a weightage of 20 marks in class 9 maths board exams.

- This chapter talks about
- Polynomials in One Variable
- Zeroes of a Polynomial
- Remainder Theorem
- Factorization of Polynomials
- Algebraic Identities

List of Exercises

Exercise 2.1 Solutions 5 Questions

Exercise 2.2 Solutions 4 Questions

Exercise 2.3 Solutions 3 Questions

Exercise 2.4 Solutions 5 Questions

Exercise 2.5 Solutions 16 Questions

## NCERT Solutions for class 9 Maths Chapter 2- Polynomials

NCERT solutions for class 9 maths chapter 2 â€“ Number System is the first chapter of class 9 Maths. Number System is introduced and discussed in detail here. The chapter discusses the Polynomials and their applications. The introduction of the chapter includes whole numbers, integers, and rational numbers.

The chapter starts with the introduction of Polynomials in section 2.1 followed by two very important topics in section 2.2 and 2.3

- Polynomials in one Variable â€“ Discussion of Linear, Quadratic and Cubic Polynomial.
- Zeroes of a Polynomial â€“ A zero of a polynomial need not be zero and can have more than one zero.
- Real Numbers and their Decimal Expansions â€“ Here you study the decimal expansions of real numbers and see whether it can help in distinguishing between rational and irrationals.

Next, it discusses the following topics.

- Representing Real Numbers on the Number Line â€“ In this the solutions for 2 problems in Exercise 2.4.
- Operations on Real Numbers â€“ Here you explore some of the operations like addition, subtraction, multiplication, and division on the irrational numbers.
- Laws of Exponents for Real Numbers â€“ Use these laws of exponents to solve the questions.

### Key advantages of NCERT Solutions for class 9 Maths Chapter 2- Polynomials

- These NCERT Solutions for class 9 Maths helps you solve and revise the whole syllabus of class 9.
- After going through the stepwise solutions given by our subject expert teachers, you will be able to score more marks.
- It follows NCERT guidelines which help in preparing the students accordingly.
- It contains all the important questions from the examination point of view.
- It helps in scoring well in maths in board exams.