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801.

If the expression (px3 + x2 – 2x – q) is divisible by (x – 1) and (x + 1), then the values of p and q respectively are ?(a) 2, – 1 (b) –2, 1 (c) –2, –1 (d) 2, 1

Answer»

(d) 2, 1

px3 + x2 – 2x – q is divisible by (x – 1) and (x + 1) 

⇒ p(1)3 + (1)2 – 2(1) – q = 0 ⇒ p – q = 1               ...(i) 

and p(–1)3 + (–1)2 – 2(–1) – q = 0 ⇒ p + q = 3        ...(ii) 

Solving (i) and (ii) p = 2, q = 1.

802.

Write the degree of the polynomial for each of the following. i. 5 + 3x4 ii. 7 iii. ax7 + bx9 (a, b are constants)

Answer»

i. 5 + 3x4

Here, the highest power of x is 4. 

∴Degree of the polynomial = 4 

ii. 7 = 7x° 

∴ Degree of the polynomial = 0

 iii. ax7+ bx9 

Here, the highest power of x is 9.

∴Degree of the polynomial = 9

803.

(2x – 3y)3 + (3y – 4z)3 + (4z – 2x)3 can be factorised into which one of the following ?(a) (2x + 3y + 4z) (2x – 3y – 4z) (b) (2x + 3y – 4z) (2x – 3y + 4z) (c) (2x – 3y) (3y – 4z) (4z – 2x) (d) 6 (2x – 3y) (3y – 4z) (2z – x)

Answer»

(d) 6.(2x – 3y)(3y – 4z)(2z – x).

Since (2x – 3y) + (3y – 4z) + (4z – 2x) = 0, therefore, 

(2x – 3y)3 + (3y – 4z)3 + (4z – 2x)3         (Take out 2 common)

= 3.(2x – 3y)(3y – 4z) (4z – 2x) 

= 6.(2x – 3y)(3y – 4z)(2z – x).

804.

For what value of k, will the expression (3x3 – kx2 + 4x + 16) be divisible by (x –\(\frac{k}{2}\)) ?(a) 4 (b) –4 (c) 2 (d) 0

Answer»

(b) – 4.

Let f(x) = 3x3 – kx2 + 4x + 16. Then, f(x) will be divisible by \(\big(\)x – \(\frac{k}{2}\)\(\big)\) if f\(\big(\frac{k}{2}\big)\) = 0 

⇒ 3.\(\big(\frac{k}{2}\big)\)3 – k.\(\big(\frac{k}{2}\big)\)2 + 4\(\big(\frac{k}{2}\big)\) + 16 = 0

⇒ \(\frac{3k^3}{8}\) - \(\frac{k^3}{4}\) + \(\frac{4k}{2}\) + 16 = 0

⇒ \(\frac{3k^3-2k^3+16k+128}{8}\) = 0

⇒ k3 + 16k + 128 = 0 ⇒ (k + 4) (k2 – 4k + 32) = 0 

⇒ k + 4 = 0 ⇒ k = – 4.

805.

If p (x) = x2 – 4x + 3, then evaluate p(2) – p (-1) + p ( ½).

Answer»

Given that,

p() =x2 – 4x + 3

According to the question,

When x = 2,

p(x) = p(2)

p() =x2 – 4x + 3

Substituting x = 2,

p(2) = (2)2 – 4(2) + 3

= 4 – 8 + 3

= – 4 + 3

= – 1

When x = – 1,

p(x) = p(– 1)

p() =x2 – 4x + 3

Substituting x = – 1,

p(– 1) = (– 1)2 – 4(– 1) + 3

= 1 + 4 + 3

= 8

When x = ½ ,

p(x) = p(½)

p() =x2 – 4x + 3

Substituting x = ½,

p(½) = (½)2 – 4(½) + 3

= ¼ – 2 + 3

= ¼ + 1

= 5/4

Now,

p(2)− p(−1) + p(½) = – 1 – 8 + (5/4)

= – 9 + (5/4)

= ( – 36 + 5)/4

= – 31/4

806.

If p(x) = x3 + 2x2 – 3x + 1 and q(x) = x3 – 2x2 + 3x + 5(a) Find p(x) + q(x). What is its degree?(b) Find p(x) – q(x). What is its degree?

Answer»

(a) p(x) = x3 + 2x2 – 3x + 1,

q(x) = x3 – 2x2 + 3x + 5

p(x) + q(x)

= x3 + 2x2 – 3x + 1 + x3 – 2x2 + 3x + 5

= 2x3 + 6

Degree = 3

(b) p(x) – q(x)

= x3 + 2x2 – 3x + 1 – (x3 – 2x2 + 3x + 5)

= x3 + 2x2 – 3x + 1 -x3 + 2x2 – 3x – 5

= 4x2 – 6x – 4

Degree = 2

807.

If x3 + px + q and x3 + qx + p have a common factor, then which of the following is correct ?(a) p + q = 0 (b) p + q – 1 = 0 (c) (p + q + 1) = 0 (d) p – q + 1 = 0

Answer»

(c) (p + q + 1) = 0.

Let the common factor be x – α, then x = α will make the given expressions zero, i.e., 

α2 + pα + q = 0

α2 + qα + p = 0 

Solving by the rule of cross-multiplication, we have

\(\frac{α^2}{p^2-q^2}\) = \(\frac{α}{q-p}\) = \(\frac{1}{q-p}\)

From, last two relation, α = 1.

⇒ α\(\frac{p^2-q^2}{q-p}\) ⇒ 1 = – (p + q) ⇒ p + q + 1 = 0.

808.

Find the value of k, if `x-1`is a factor of p(x) in each of the following cases:(i) `p(x)=x^2+x+k` (ii) `p(x)=2x^2+k x+sqrt(2)`(iii) `p(x)=k x^2-sqrt(2)x+1`(iv) `p(x)=k x^2-3x+k`

Answer» Here, `(x-1)` is a factor of ` p(x)` that means from Factor theorem,
`p(1) = 0.`
`(i) p(x) = x^2+x+k`
As, `p(1)` is `0`
`0 = 1^2+1+k=>k=-2`

`(ii) p(x) = 2x^2+kx+sqrt2`
As, `p(1)` is `0`
`2+k+sqrt2 = 0=>k = -(2+sqrt(2))`

`(iii) p(x) = kx^2-sqrt2x+1`
As, `p(1)` is `0`
`k-sqrt2+1 = 0=>k = sqrt2-1`

`(iv) p(x) = kx^2-3x+k`
As, `p(1)` is `0`
`k-3+k=0 =>2k = 3`
`k=3/2`
809.

Find the value of the polynomial 3x3 – 4x2 + 7x – 5, when x = 3 and also when x = -3.

Answer»

Given that,

p(x) = 3x3 – 4x2 + 7x – 5

According to the question,

When x = 3,

p(x) = p(3)

p(x) = 3x3 – 4x2 + 7x – 5

Substituting x = 3,

p(3)= 3(3)3 – 4(3)2 + 7(3) – 5

p(3) = 3(3)3 – 4(3)2 + 7(3) – 5

= 3(27) – 4(9) + 21 – 5

= 81 – 36 + 21 – 5

= 102 – 41

= 61

When x = – 3,

p(x) = p(– 3)

p(x) = 3x3 – 4x2 + 7x – 5

Substituting x = – 3,

p(– 3)= 3(– 3)3 – 4(– 3)2 + 7(– 3) – 5

p(– 3) = 3(–3)3 – 4(–3)2 + 7(–3) – 5

= 3(–27) – 4(9) – 21 – 5

= –81 – 36 – 21 – 5

= –143

810.

In the polynomial p(x) = 3x2 – ax + 1,Find ‘a’ satisfying p(1) = 2.

Answer»

p(x) = 3x2 – ax + 1

p(1) = 3(1)2 – (a × 1) + 1 = 3 – a + 1 = 4 – a

Given p(1) = 2

That is, 4 – a = 2 , a = 4 – 2 = 2

811.

The sum of \((\frac{x-1}{x+1})\) and its reciprocal is ………………A) \(\frac{x^2+1}{x^2-1}\)B) \(\frac{2(x^2+1)}{x^2-1}\)C) \(\frac{x^2-1}{x^2+1}\)D) \(\frac{2(x^2-1)}{x^2+1}\)

Answer»

Correct option is (B) \(\frac{2(x^2+1)}{x^2-1}\)

Sum of \(\left(\frac{x-1}{x+1}\right)\) and its reciprocal \(=\frac{x-1}{x+1}+\frac{x+1}{x-1}\)

\(=\frac{(x-1)^2+(x+1)^2}{(x+1)(x-1)}\) \(=\frac{(x^2-2x+1)+(x^2+2x+1)}{x^2-1}\)

\(=\frac{2(x^2+1)}{x^2-1}\)

Correct option is  B) \(\frac{2(x^2+1)}{x^2-1}\)

812.

What is/are the factors of (x29 – x24 + x13 – 1) ?(a) (x – 1) only (b) (x + 1) only (c) (x – 1) and (x + 1) (d) Neither (x – 1) nor (x + 1)

Answer»

(a) (x – 1) only

For (x – 1) to be a factor of the given expression, the value of expression at x = 1 is 

(1)29 – (1)24 + (1)13 – 1 = 1 – 1 + 1 – 1 = 0 

∴ (x – 1) is a factor of x29 – x24 + x13 – 1 

Similarly for (x + 1) to be the factor, the value of expression at x = – 1 is 

(–1)29 – (–1)24 + (–1)13 – 1 = – 1 – 1 – 1 – 1 = – 4 ≠ 0 

∴ (x + 1) is not a factor of x29 – x24 + x13 – 1. 

Hence, (a) is the correct option.

813.

7x3 – 4x2 – x + 4 is a polynomial.a. Write the terms of the polynomial.b. Write the coefficient of x2.c. Write the constant terms of the polynomial.d. What is the degree of the polynomial ?

Answer»

a. Terms = 7x2, -4x2, -x, 4

b. Coefficient of x2 = -4

c. Constant term = 4

d. Degree of the polynomial = 3

814.

The value of 6a + 11b if x3 – 6x2 + ax + b is exactly divisible by (x2 – 3x + 2) is ………………A) 0 B) 66 C) 132 D) 1

Answer»

Correct option is (A) 0

\(\because\) (x - 1) & (x - 2) are factors of \((x^3 – 6x^2 + ax + b)\)

\((\because\) (x - 1) (x - 2) \(=x^2-3x+2)\)

\(\therefore\) x = 1 and x = 2 are zeros of \((x^3 – 6x^2 + ax + b)\)

\(\therefore\) 1-6+a+b = 0 and 8-24+2a+b = 0

\(\Rightarrow\) a+b = 5 and 2a+b = 16

\(\Rightarrow\) (2a+b) - (a+b) = 16 - 5

\(\Rightarrow\) a = 11

\(\therefore\) b = 5 - a = 5 - 11 = -6

\(\therefore\) 6a+11b \(=6\times11+11\times-6\)

= 66 - 66 = 0

Correct option is A) 0

815.

Find “a” and “b” in order that x3 – 6x2 + ax + b may be exactly divisible by x2 – 3x + 2. A) a = 11, b = -5 B) a = 11, b = 6 C) a = 11, b = -6 D) a = -11, b = -5

Answer»

Correct option is (C) a = 11, b = -6

\((x^2 – 3x + 2)\) is a factor of \((x^3-6x^2+ax+b)\)

\(\Rightarrow\) (x-1) & (x-2) are factors of \((x^3-6x^2+ax+b)\)

\((\because\) (x-1) (x-2) \(=x^2 – 3x + 2)\)

\(\Rightarrow\) x = 1 & x = 2 are zeros of \((x^3-6x^2+ax+b)\)

\(\therefore\) 1 - 6 + a + b = 0 and 8 - 24 + 2a + b = 0

\(\Rightarrow\) a+b = 5 and 2a+b = 16

\(\Rightarrow\) (2a+b) - (a+b) = 16 - 5

\(\Rightarrow\) a = 11

\(\therefore\) b = 5 - a = 5 - 11 = -6

Correct option is B) a = 11, b = 6

816.

If the expressions (px3 + 3x2 – 3) and (2x3 – 5x + p) when divided by (x – 4) leave the same remainder, then what is the value of p ?

Answer»

Let f(x) = px3 + 3x2 – 3 

g(x) = 2x3 – 5x + p 

When divisible by x – 4, the remainders for the given expressions are f(4) and g(4) respectively. 

f(4) = p(4)3 + 3(4)2 – 3 = 64p + 48 – 3 = 64p + 45 

g(4) = 2(4)3 – 5(4) + p = 128 – 20 + p = 108 + p. 

Given, f(4) = g(4) ⇒ 64p + 45 = 108 + p ⇒ 63 p = 63 ⇒ p = 1.

817.

Simplify the followingi. (2x + 1) (3x + 4) (4x + 3) (3x + 4)ii. (3x + 4)2 – (2x – 1) (3x + 4)

Answer»

i. (2x + 1) (3x + 4) (4x + 3) (3x + 4)

= (3x + 4) [(2x + 1 + 4x + 3)]

= (3x + 4) [6x + 4]

= (3x x (6x) + (3x) x (4)+ 4x(6x) + 4 x 4

= 18x2 + 12x + 24x + 16

= 18x2 + 36x + 16

ii. (3x + 4)2 – (2x – 1) (3x + 4)

= (3x + 4) [3x + 4 – (2x – 1)]

= (3x + 4)[3x + 4 – 2x + 1] = (3x + 4) (x + 5)

= 3x2 + 15x + 4x + 20

= 3x2 + 19x + 20

818.

If x5 – 9x2 + 12x – 14 is divisible by (x – 3), what is the remainder ?

Answer»

Let f(x) = x5 – 9x2 + 12x – 14 

f(x) is divisible by (x – 3) so remainder = f(3). 

∴ f(3) = (3)5 – 9(3)2 + 12(3) – 14 = 243 – 81 + 36 – 14 = 184.

819.

In a polynomial p(x) = 2x3 – 7x2 + kx + 20,p(2) = p(3).a. Find the value of k. b. Using the value of k, write the polynomial. c. Find p(1).

Answer»

a. p(2) = 2 × 22 – 7 × 22 + k × 2 + 20

= 16 – 28 + 2k + 20 = 8 + 2k

p(3) = 2 × 33 – 7 × 32 + k × 3 + 20

= 54 – 63 + 3k + 20 = 11 + 3k

P(2) = P(3)

8 + 2k = 11 + 3k

k = -3

b. p(x) = 2x3 – 7x2 - 3x + 20

c. p(1) = 2 – 7 – 3 + 20 = 12

820.

Find the remainder when `x^(3)-ax^(2)+6x-a` is divided by x-a.

Answer» The zero of x-a is a.
Let `p(x)=x^(3)-ax^(2)+6x-a`
So, `p(a)=a^(3)-a(a)^(2)+6a-a=a^(3)-a^(3)+5a`
`implies p(a)=5a`
`therefore` Required remainder =5a
821.

Find the remainder when x4 + 15x3 + 6x2 – 12x + 3 is divided by x + 2 ? ……………A) -101B) 53 C) -52 D) 52

Answer»

Correct option is (A) -101

Let \(p(x)=x^4+15x^3+6x^2+12x+3\)

Remainder when p(x) is divided by x+2 is

\(p(-2)=(-2)^4+15(-2)^3\) \(+6(-2)^2+12(-2)+3\)

= 16 - 120 + 24 - 24 + 3 = -101

Correct option is A) -101

822.

In a polynomial p(x) = 2x3 + 9x2 + kx + 3, p(-2) = p(-3). Find the value of k.

Answer»

p(x) = 2x3 + 9x2 + kx + 3

p(-2) = 2(-2)3 + 9(-2)2 + k(-2) + 3

= -16 + 36 – 2k + 3 = 23 – 2k

p(-3) = 2(-3)3 + 9(-3)2 + k(-3) + 3

= -54 + 81 – 3k + 3 = 30 – 3k

We have p(-2) = p(-3),

23 -2k = 30 -3k

-2k + 3k = 30 – 23

k = 7

823.

In a polynomial p(x) = 2x3 + ax2 – 7x + b. p(1) = 3, p(2) = 19. Then find the value of ‘a’ and ‘b’?

Answer»

p(x) = 2x3 + ax2 – 7x + b

We have p(1) = 3.

p(1) = 2 x 13 + a x 12 – 7 x 1 + b = 3

2 + a – 7 + b = 3

a + b – 5 = 3

a + b = 8 ………. (1)

We have p(2) = 19.

p(2 ) = 2 x 23 + a x 22 – 7 x 2 + b = 19

16 + 4a – 14 + b = 19

4a + b + 2 = 19

4a + b = 17…….. (2)

From equation (1), (2)

(2) – (1) 4a + b = 17

\(\frac{a+b=8}{3a=9}\)

a = 9/3 = 3

From equation (1)

a + b = 8

3 + b = 8

b = 5

824.

Use the Factor Theorem to determine whether g(x) is a factor of p(x) in each of the following cases : (i) p(x) = 2x3 + x2 – 2x – 1, g(x) = x+1 (ii) p(x) = x3 + 3x2 + 3x + 1, g(x) = x + 2 (iii) p(x) = x3 – 4x2 + x + 6, g(x) = x – 3

Answer»

(i) p(x) = 2x3 + x2 – 2x – 1 

g(x) = x + 1 

If x + 1 = 0, then x = -1 

p(x) = 2x3 + x2 – 2x – 1 

p(-1)= 2(-1)3 + (-1)2 -2(- 1) – 1 

= 2(-1) + (1) + 2 – 1 = -2 + 1 + 2 – 1 

P(-1)= 0 

Here, r(x) = p(a) = 0, 

∴ g(x) is the a factor f(x) 

(ii) p(x) = x3 + 3x2 + 3x + 1 

g(x) = x + 2 

If x + 2 = 0, then x = -2 

∴ p(x) = x3 + 3x2 + 3x + 1 

p(-2) = (-2)3 + 3(-2)2 + 3 (-2) + 1 

= -8 + 3(4) + 3(-2) + 1 

= -8 + 12 – 6 + 1 

= 13 – 24 

p(-2)= -11 

Here we have r(x) = p(a) =-11. 

Value of r(x) is not equal to zero. 

∴ g(x) is not a factor of f(x). 

(iii) p(x) = x3 – 4x2 + x + 6 

g(x) = x – 3 

Let, x – 3 = 0, then x = 3 

p(x) = x3 – 4x2 + x + 6 

p(3) = (3)2 – 4(3)2 + 3 + 6 

= 27 – 4(9) + 3 + 6 

= 27 – 36 + 3 + 6 = 36 – 36 

p(3) = 0 

Here, we have r(x) = p(a) = 0 

∴ (x – 3) is the factor of p(x).

825.

Determine which of the following polynomials has (x+1) a factor : (i) x3 + x2 + x + 1 (ii) x4 + x3 + x2 + x + 1 (iii) x4 + 3x3 + 3x2 + x + 1 (iv) x3 – x2 – (2 + √2)x + √2

Answer»

(i) x- 1 is a factor of p(x) 

x + 1 = x – a 

a = -1 

For the value of p(a), 

value of r(x) = 0. 

∴ p(x) = x3 + x2 + x + 1

p(-1)= (-1)3 + (-1)2 + (-1) + 1 

= -1 + 1 -1 + 1 

p(-1)= 0 

Here, p(a) = r(x) = 0 

∴ x + 1 is a factor. 

(ii) If x + 1 = x – a, then a = -1 

p(x) = x4 + x3 + x2 + x + 1 

p(-1)= (-1)4 + (-1)3 +(-1)2 + (-1)+ 1 

= 1 – 1 + 1 – 1 + 1 

= 3 – 2 p(-1)= 1 

Here, r(x) = p(a)= 1 

Reminder is not zero. 

∴ x+1 is not a factor. 

(iii) If x + 1 = x – a then a = -1 

p(x) = x4 + 3x3 + 3x2 + x + 1 

p(-1) = (-1)4 + 3(-1 )3 +3(-1 )2 + (-1) + 1 

= 1 + 3(-1) + 3(1) + 1(-1) + 1 

= 1- 3 + 3 – 1 + 1 

= 5 – 4 P(-1)= 1 

Here, r(x) = p(a) = 1 

Remainder is not zero 

∴ x+1 is not a factor. 

(iv) If x + 1 = x – a then, 

a = -1 

p(x) = x3 – x2 – (2 + √2)x+ p(-1) 

= (-1)3 – (-1)2 -(2 + √2)(-1) + √2 

= -1 -(+1) – (2 – √2) + √2

= -1 – 1 + 2 + √2 +√2  

= -2 + 2 + √2 

= + 2√2

p(-1) = 2√2

Here, r(x) = p(a) = 2√2 Value of remainder r(x) is not zero. 

∴ x + 1 is not a factor.

826.

Find p(0), p(1) and p(-1) in the following polynomials,i. p(x) = 3x + 5ii. p(x) = 3x2 + 6x + 1iii. p(x) = 2x2 – 3x + 4iv. p(x) = 4x3 + 2×2 + 3x + 7v. p(x) = 5x3 – x2 + 2x – 3

Answer»

i. p(x) = 3x + 5 

p(0) = 3 × 0 + 5 = 5 

p(1) = 3 × 1 + 5 = 8 

p(-1) = 3 x - 1 + 5 = 2

ii. p(x) = 3x2 + 6x + 1 

p(0) = 3 × 02 + 6 × 0 + 1 = 1

p(1) = 3 × 12 + 6 × 1 + 1 = 10 

p(-1) = 3 × (-1)2 + 6 × (-1) + 1 = -2

iii. p(x) = 2x2 – 3x + 4 

p(0) = 2 × 02 – 3 × 0 + 4 = 4 

p(1) = 2 × 12 – 3 × 1 + 4 = 3 

p(-1) =2 × (-1)2 – 3 × (-1) + 4 = 9

iv. p(x) = 4x3 + 2x2 + 3x + 7 

p(0) = 4 × 03 + 2 × 02 + 3 × 0 +7 = 7 

p(1) = 4 × 13 + 2 × 12 + 3 × 1 + 7 = 16 

p(-1) = 4 × (-1)3 + 2 × (-1)2 + 3 × (-1) +7 = 2

v. p(x) = 5x3 – x2 + 2x – 3 

p(0) = 5 × 03 – 02 + 2 × 0 – 3 =-3 

p(1) = 5 × 13 – 12 + 2 × 1 – 3 = 3 

p(-1) = 5 × (-1)3 – (-1)2 + 2 × (-1) – 3 = -11

827.

Find p(1) and p(10) in the following polynomials,i. p(x) = 2x + 5 ii. p(x) = 3x2 + 6x + 1 iii. p(x) = 4x3 + 2x2 + 3x + 7

Answer»

i. p(x) = 2x + 5 

p(1) = 2 × 1 + 5 = 2 + 5 = 7 

p(10) = 2 × 10 + 5 = 20 + 5 = 25

ii. p(x) = 3x2 + 6x + 1 

p(1) = 3 × 12 + 6 x 1 + 1 

= 3 + 6 + 1 = 10 

p(10) = 3 × 102 + 6 × 10 + 1 = 300 + 60 + 1 = 361

iii. p(x) = 4x3 + 2x2 + 3x + 7 

p(1) = 4 × 13 + 2 × 12 + 3 × 1 + 7

= 4 + 2 + 3 + 7 = 16 

p(10) = 4 × 103 + 2 × 102 + 3 × 10 + 7 

= 4000 + 200 + 30 + 7 = 4237

828.

Factorize the polynomials. (x2 – 6x)2 – 8(x2 – 6x + 8) – 64 

Answer»

(x2 – 6x)2 – 8(x2 – 6x + 8) – 64 

= m2 – 8(m + 8)-64 …[Putting x2 – 6x = m] 

= m2 – 8m – 64 – 64 

= m2 – 8m – 128

= m2 – 16m + 8m- 128 

= m(m – 16) + 8(m – 16) 

= (m – 16)(m + 8)

 = (x2 – 6x – 16) (x2 – 6x + 8) … [Replacing m = x2 – 6x] 

= (x2 – 8x + 2x – 16) (x2 – 4x – 2x + 8) 

= [x(x – 8) + 2(x – 8)] [x(x – 4) – 2(x – 4)] 

= (x – 8) (x + 2) (x – 4) (x – 2)

829.

Evaluate the products without actual multiplication :101 x 99

Answer»

101 x 99 

= (100 + 1) (100 – 1) 

= 1002 – 12 

= 10000 – 1 

= 9999

830.

Factorize the polynomials.(y + 2) (y – 3) (y + 8) (y + 3) + 56

Answer»

(y + 2) (y – 3) (y + 8) (y + 3) + 56 

= (y + 2)(y + 3)(y – 3)(y + 8) + 56 

= (y2 + 3y + 2y + 6) (y2 + 8y – 3y – 24) + 56 

= (y2 + 5y + 6) (y2 + 5y – 24) + 56 

= (m + 6) (m – 24) + 56 … [Putting y2 + 5y = m]

= m (m – 24) + 6 (m – 24) + 56 

= m2 – 24m + 6m – 144 + 56

 = m2 – 18m – 88 

= m2 – 22m + 4m – 88

 = m(m – 22) + 4(m – 22)

 = (m – 22) (m + 4) 

= (y2 + 5y – 22)(y2 + 5y + 4) … [Replacing m = y2 + 5y] 

= (y2 + 5y – 22) (y2 + 4y + y + 4) 

= (y2 + 5y – 22) [y(y + 4) + 1(y + 4)] 

= (y2 + 5y – 22) (y + 4) (y + 1)

831.

Number of zeroes of x2 – 7x + 12 is ……………A) 4 B) 7 C) 2 D) 1

Answer»

Correct option is (C) 2

\(x^2 – 7x + 12=0\)

\(\Rightarrow\) (x - 3) (x - 4) = 0

\(\Rightarrow\) x = 3 or x = 4

\(\therefore\) Number of zeros of \(x^2 – 7x + 12\) is 2.

Correct option is C) 2

832.

Divide p(x) by g(x) in each of the following questions and find the quotient q(x) and remainder r(x) : `p(x)=x^(4)+6x^(3)-4x^(2)+2x+1, " " g(x)=x^(2)+3x-1`

Answer» Correct Answer - `q(x)=x^(2)+3x-12, " "r(x)=41x-11`
833.

The product of two consecutive numbers is 56. Find ……………A) -8, -7B) 8, -7C) -8, 7D) 8, 7

Answer»

Correct option is (A) -8, -7

Let consecutive numbers are x & (x+1).

\(\therefore\) x (x+1) = 56

\(\Rightarrow\) \(x^2+x-56=0\)

\(\Rightarrow\) \(x^2+8x-7x-56=0\)

\(\Rightarrow\) x (x+8) - 7 (x+8) = 0

\(\Rightarrow\) (x-7) (x+8) = 0

\(\Rightarrow\) x = 7 or x = -8

\(\therefore\) Consecutive numbers either -8, -7 or 7, 8.

Correct option is A) -8, -7

834.

Expand : (i) `(4a-5b)^(3) " " (ii) (a+2b)^(3)`

Answer» `(i) (4a-5b)^(3)=(4a)^(3)-(5b)^(3)-3xx4axx5b(4a-5b)`
`=64a^(3)-125b^(3)-60ab(4a-5b)=64a^(3)-125b^(3)-240a^(2)b+300ab^(2)`
`(ii) (a+2b)^(3)=(a)^(3)+(2b)^(3)+3xxaxx2b(a+2b)`
`=a^(3)+8b^(3)+6ab(a+2b)=a^(3)+8b^(3)+6a^(2)b+12ab^(2)`
835.

If we divide 36x2 – 12x + 1- 49y2 by 6x + 7y -1, then the quotient is ……………… A) 6x + 1 + 7y B) 6x – 1 – 7y C) 6x + 2 + 7y D) -6x -1 – 7y

Answer»

Correct option is B) 6x – 1 – 7y

836.

Find the product using appropriate identities (i) (x+5)(x+5) (ii) (x+4)(x-4) (iii) (x+5)(x+3) (iv) (x-5)(x+3)

Answer» (i) We know that `(x+y)^(2)=x^(2)+2xy+y^(2)`
Now, `(x+5)(x+5)=(x+5)^(2)=x^(2)+2xx x xx5+5^(2)=x^(2)+10x+25`
(ii) We know that `(x+a)(x-a)=x^(2)-a^(2)`
Now, `(x+4)(x-4)=x^(2)-4^(2)=x^(2)-16`
(iii) We know that `(x+a)(x+b)=x^(2)+(a+b)x+ab`
Now, `(x+5)(x+3)=x^(2)+(5+3)x+5xx3=x^(2)+8x+15`
(iv) We know that `(x-a)(x+b)=x^(2)+(-a+b)x+(-a)xxb`
Now, `(x-5)(x+3)=x^(2)+(-5+3)x+(-5)xx3=x^(2)-2x-15`
837.

Factorise : `(i) 36x^(2)+60xy+25y^(2) (ii) (49)/(9)x^(2)-(35)/(6)xy+(25)/(16)y^(2)`

Answer» `(i) 36x^(2)+60xy+25y^(2)`
We can write it `(6x)^(2)+2xx6xx5y+(5y)^(2)=(6x+5y)^(2)`
`=(6x+5y)(6x+5y)`
(ii) `(49)/(9)x^(2)-(35)/(6)xy+(25)/(16)y^(2)`
We can write it `((7)/(3)x)^(2)-2xx(7)/(3)x xx(5)/(4)y+((5)/(4)y)^(2)`
`=((7)/(3)x-(5)/(4)y)^(2)=((7)/(3)x-(5)/(4)y)((7)/(3)x-(5)/(4)y)`
838.

If A = \(\frac{2x+1}{2x-1}\) and B = \(\frac{2x-1}{2x+1},\) then A - B is equal to :(a) \(\frac{1}{4x^2-1}\)(b) \(\frac{8}{4x^2-1}\)(c) \(\frac{-2}{4x^2-1}\)(d) \(\frac{4x}{4x^2-1}\)

Answer»

(b) \(\frac{8}{4x^2-1}\)

A - B = \(\frac{2x+1}{2x-1}\) - \(\frac{2x-1}{2x+1}\)

\(\frac{(2x+1)^2 -(2x-1)^2}{(2x-1)(2x+1)}\)

\(\frac{(4x^2+4x+1)-(4x^2-4x+1)}{4x^2-1}\)

\(\frac{8}{4x^2-1}\)

839.

\(\frac{1}{x+1}-\frac{1}{x-1}-\frac{x^2}{x+1}+\frac{x^2}{x-1},\) when simplified is equal to :(a) 0 (b) 1 (c) 2 (d) –2

Answer»

(c) 2

\(\frac{1}{x+1}-\frac{1}{x-1}-\frac{x^2}{x+1}+\frac{x^2}{x-1}\)

\(\frac{(x-1)-(x+1)-x^2(x-1)+x^2(x+1)}{(x-1)(x+1)}\)

\(\frac{x-1-x-1-x^3+x^2+x^3+x^2}{x^2-1}\)

\(\frac{2x^2-2}{x^2-1}=\frac{2(x^2-1)}{(x^2-1)}\) = 2

840.

\(\bigg(\frac{2x+y}{x+y}-1\bigg)÷\bigg(1-\frac{y}{x+y}\bigg)\) id equal to :(a) x (b) y (c) xy (d) 1

Answer»

(d) 1

\(\bigg(\frac{2x+y}{x+y}-1\bigg)÷\bigg(1-\frac{y}{x+y}\bigg)\)

\(\bigg[\frac{2x+y-(x+y)}{x+y}\bigg]÷\bigg[\frac{x+y-y}{x+y}\bigg]\)

\(\frac{x}{x+y}\times\frac{x+y}{x}=1\)

841.

The HCF of two polynomials \(4x^2(x^2 - 3x + 2)\) and \(12x(x - 2)(x^2 - 4)\) is 4x(x - 2). The LCM of the two polynomials is : (a) 12x (x2 - 4)(b) 12x2 (x2 - 3x + 4)(x2 - 2)(c) 12x2 (x2 - 3x + 2)(x2 - 4)(d) 12x(x2 - 3x - 2)(x2 - 4)

Answer»

(c) 12x2(x2 - 3x +2)(x2 - 4)

LCM = \(\frac{\text{product of the polynomials}}{HCF}\)

\(\frac{4x^2(x^2-3x+2)\times12x(x-2)(x^2-4)}{4x(x-2)}\)

\(\frac{4x^2(x-2)(x-1)\times12x(x-2)(x-2)(x+2)}{4x(x-2)}\)

= 12x2(x - 1)(x - 2)(x - 2)(x + 2)

= 12x2(x2 - 3x +2)(x2 - 4)

842.

The LCM of the polynomials \(x^3 + 3x^2 +3x +1\), \(x^2 + 2x + 1\) and \(x^2 - 1\) is:(a) (x2 - 1)(x + 1)3(b) (x2 + 1)(x - 1)2(c) (x2 - 1)(x - 1)2(d) (x + 1)3

Answer»

(a) (x2 - 1)(x + 1)3

\(x^3 + 3x^2 +3x +1\) = (x + 1)3

\(x^2 + 2x + 1\) = (x + 1)2

\(x^2 - 1\) = (x + 1)(x - 1)

∴ Reqd. LCM = (x - 1)(x + 1)3

= (x2 - 1)(x + 1)3

843.

The product of the rational expressions \(\frac{x^2 - y^2}{x^2+2xy+y^2}\) and \(\frac{xy+y^2}{x^2 - xy}\) is :(a) xy (b) y/x (c) x/y (d) 1

Answer»

(b) \(\frac{y}{x}\)

Reqd. product = \(\frac{x^2 - y^2}{x^2+2xy+y^2}\) x \(\frac{xy+y^2}{x^2 - xy}\)

\(\frac{(x + y)(x + y)}{(x+y)^2}\times\frac{y(x+y)}{x(x-y)}\)

\(\frac{y}{x}\)

844.

If x + y + z = 0, show that x3 + y3 + z3 = 3xyz.

Answer»

x + y + z = 0 

x + y = -z 

by cubing on both sides, 

(x + y)3 = (-z)3 

x3+ y3 + 3xy(x + y) = -z3 

x3 + y3 + 3xy (-z) 

= -z (∵ x + y =-z data given) 

x3 + y3 – 3xyz = -z3 

∴ x3 + y3 + z3 = 3xyz.

845.

\(\frac{x^3+y^3+z^3-3xyz}{a^3+b^3+c^3-3abc}\times\frac{a^2+b^2+c^2-ab-bc-ca}{x^2+y^2+z^2-xy-yz-zx}\) equlas(a) 1 (b) \(\frac{x^2+y^2+z^2}{a^2+b^2+c^2}\)(c) \(\frac{x+y+z}{a+b+c}\)(d) \(\frac{xyz}{abc}\)

Answer»

(c) \(\frac{x+y+z}{a+b+c}\)

Reqd. exp.

\(\frac{(x+y+z)(x^2+y^2+z^2-xy-yz-zx)}{(a+b+c)(a^2+b^2+c^2-ab-bc-ca)}\times\frac{a^2+b^2+c^2-ab-bc-ca}{x^2+y^2+z^2-xy-yz-zx}\)

\(\frac{x+y+z}{a+b+c}\)

846.

Verify that x3 + y3 + z3 – 3xyz = 1/2 (x + y + z) [(x – y)2 + (y – z)2 + (z – x)2 ] (OR) Verify that p3 + q3 + r3 – 3pqr = 1/2 (p + q + r) [(p – q)2 + (q – r)2 + (r – p)2 ]

Answer»

Given x3 + y3 + z3 – 3xyz = 1/2 (x + y + z) [(x – y)2 + (y – z)2 + (z – x)2

R-H.S = 1/2 (x + y + z) [(x – y)2 + (y – z)2 + (z – x)2

= 1/2 (x + y + z) [x2 + y2 – 2xy + y2 + z2 – 2yz + z2 + x2 – 2xz] 

= 1/2 (x + y + z) [2x2 + 2y2 + 2z2 – 2xy – 2yz – 2zx] 

= 1/2 (x + y + z) (2) [x2 + y2 + z2 – xy – yz – zx] 

= (x + y + z) (x2 + y2 + z2 – xy – yz – zx) 

= L.H.S 

Hence proved.

847.

If x + y + z = 0, show that x3 + y3 + z3 = 3xyz

Answer»

Given x + y + z = 0 

To prove x3 + y3 + z3 = 3xyz 

We have an identity 

(x + y + z) (x2 + y2 + z2 – xy – yz – zx) 

= x3 + y3 + z3 – 3xyz 

Substituting x + y + z = 0in the above equation, we get 

0 x (x2 + y2 + z2 -xy-yz-zx) 

= x3 + y3 + z3 – 3xyz 

⇒ x3 + y3 + z3 – 3xyz = 0 

⇒ x3 + y3 + z3 = 3xyz

848.

Verify that `x^(3)+y^(3)+z^(3)-3xyz=(1)/(2)(x+y+z)[(x-y)^(2)+(y-z)^(2)+(z-x)^(2)]`

Answer» `R.H.S. = 1/2(x+y+z)[(x-y)^2+(y-z)^2+(z-x)^2]`
`=1/2(x+y+z)(x^2+y^2-2xy+y^2+z^2-2yz+z^2+x^2-2zx)`
`=1/2(x+y+z)(2x^2+2y^2+2z^2-2xy-2yz-2zx)`
`=(x+y+z)(x^2+y^2+z^2-xy-yz-zx)`
We have the formula,
`x^3+y^3+z^3 -3xyz =(x+y+z)(x^2+y^2+z^2-xy-yz-zx)`
Thus, `L.H.S. = R.H.S.`
849.

Find the zeros of the quadratic polynomials 8x2 - 4 and verify the relationship between the zeros and the coefficients.

Answer»

Let f(x) = 8x2 – 4

= 4 ((√2x)2 – (1)2)

= 4(√2x + 1)(√2x – 1)

To find the zeroes, set f(x) = 0

(√2x + 1)(√2x – 1) = 0

(√2x + 1) = 0 or (√2x – 1) = 0

x = (-1)/√2 or x = 1/√2

So, the zeroes of f(x) are (-1)/√2 and x = 1/√2

Again,

Sum of zeroes = -1/√2 + 1/√2 = (-1+1)/√2 = 0

= -b/a

= (-Coefficient of x)/(Cofficient of x2)

Product of zeroes = -1/√2 x 1/√2 = -1/2 = -4/8

= c/a

= Constant term / Coefficient of x2

850.

Simplify \(\frac{1}{1+x+x^2}\) - \(\frac{1}{1-x+x^2}\) + \(\frac{2x}{1+x^2+x^4}\).............A) \(\frac{1}{1+x^2+x^4}\)B) 0 C) \(\frac{-1}{1+x^2+x^4}\)D) \(\frac{2x-3}{1+x^2+x^4}\)

Answer»

Correct option is (B) 0

\(\frac{1}{1+x+x^2}-\frac{1}{1-x+x^2}+\frac{2x}{1+x^2+x^4}\)

\(=\frac{(1-x+x^2)-(1+x+x^2)}{(1+x^2+x)(1+x^2-x)}+\frac{2x}{1+x^2+x^4}\)

\(=\frac{-2x}{(1+x^2)^2-x^2}+\frac{2x}{1+x^2+x^4}\)

\(=\frac{-2x}{1+x^4+2x^2-x^2}+\frac{2x}{1+x^2+x^4}\)

\(=\frac{-2x}{1+x^2+x^4}+\frac{2x}{1+x^2+x^4}=0\)

Correct option is B) 0