NCERT Exemplar Solutions
Class 11 - Mathematics
Chapter 13: LIMITS AND DERIVATIVES

Limits of a function, Limits of polynomials and rational functions, Limits of trigonometric functions, Derivatives

Short Answer Type

Question. 1

Evaluate \(\displaystyle\lim_{x\to3}\dfrac{x^{2}-9}{x-3}\).

Answer:

6

Question. 2

Evaluate \(\displaystyle\lim_{x\to\tfrac{1}{2}}\dfrac{4x^{2}-1}{2x-1}\).

Answer:

2

Question. 3

Evaluate \(\displaystyle\lim_{h\to0}\dfrac{\sqrt{x+h}-\sqrt{x}}{h}\).

Answer:

\(\dfrac{1}{2\sqrt{x}}\)

Question. 4

Evaluate \(\displaystyle\lim_{x\to0}\dfrac{(x+2)^{1/3}-2^{1/3}}{x}\).

Answer:

\(\dfrac{1}{3}2^{-2/3}\)

Question. 5

Evaluate \(\displaystyle\lim_{x\to1}\dfrac{(1+x)^{6}-1}{(1+x)^{2}-1}\).

Answer:

3

Question. 6

Evaluate \(\displaystyle\lim_{x\to-1}\dfrac{x^{3}+27}{x+1}\).

Answer:

3

Question. 7

Evaluate \(\displaystyle\lim_{x\to1}\dfrac{x^{4}-\sqrt{x}}{\sqrt{x}-1}\).

Answer:

7

Question. 8

Evaluate \(\displaystyle\lim_{x\to2}\dfrac{x^{2}-4}{\sqrt{3x-2}-\sqrt{x+2}}\).

Answer:

8

Question. 9

Evaluate \(\displaystyle\lim_{x\to\sqrt{2}}\dfrac{x^{4}-4}{x^{2}+3\sqrt{2}x-8}\).

Answer:

\(\dfrac{8}{5}\)

Question. 10

Evaluate \(\displaystyle\lim_{x\to1}\dfrac{x^{7}-2x^{5}+1}{x^{3}-3x^{2}+2}\).

Answer:

1

Question. 11

Evaluate \(\displaystyle\lim_{x\to0}\dfrac{\sqrt{1+x^{3}}-\sqrt{1-x^{3}}}{x^{2}}\).

Answer:

0

Question. 12

Evaluate \(\displaystyle\lim_{x\to-3}\dfrac{x^{3}+27}{x^{5}+243}\).

Answer:

\(\dfrac{1}{15}\)

Question. 13

Evaluate \(\displaystyle\lim_{x\to\tfrac{1}{2}}\left(\dfrac{8x-3}{2x-1}-\dfrac{4x^{2}+1}{4x^{2}-1}\right)\).

Answer:

\(\dfrac{7}{2}\)

Question. 14

Find \(n\in\mathbb{N}\) if \(\displaystyle\lim_{x\to2}\dfrac{x^{n}-2^{n}}{x-2}=80\).

Answer:

\(n=5\)

Question. 15

Evaluate \(\displaystyle\lim_{x\to a}\dfrac{\sin3x}{\sin7x}\).

Answer:

\(\dfrac{3}{7}\)

Question. 16

Evaluate \(\displaystyle\lim_{x\to0}\dfrac{\sin^{2}2x}{\sin^{2}4x}\).

Answer:

\(\dfrac{1}{4}\)

Question. 17

Evaluate \(\displaystyle\lim_{x\to0}\dfrac{1-\cos2x}{x^{2}}\).

Answer:

2

Question. 18

Evaluate \(\displaystyle\lim_{x\to0}\dfrac{2\sin x-\sin2x}{x^{3}}\).

Answer:

1

Question. 19

Evaluate \(\displaystyle\lim_{x\to0}\dfrac{1-\cos mx}{1-\cos nx}\).

Answer:

\(\dfrac{m^{2}}{n^{2}}\)

Question. 20

Evaluate \(\displaystyle\lim_{x\to\tfrac{\pi}{3}}\sqrt{2}\left(\dfrac{\pi}{3}-x\right)\sqrt{1-\cos6x}\).

Answer:

3

Question. 21

Evaluate \(\displaystyle\lim_{x\to\tfrac{\pi}{4}}\dfrac{\sin x-\cos x}{x-\tfrac{\pi}{4}}\).

Answer:

\(\sqrt{2}\)

Question. 22

Evaluate \(\displaystyle\lim_{x\to\tfrac{\pi}{6}}\dfrac{\sqrt{3}\sin x-\cos x}{x-\tfrac{\pi}{6}}\).

Answer:

2

Question. 23

Evaluate \(\displaystyle\lim_{x\to0}\dfrac{\sin2x+3x}{2x+\tan3x}\).

Answer:

1

Question. 24

Evaluate \(\displaystyle\lim_{x\to a}\dfrac{\sin x-\sin a}{\sqrt{x}-\sqrt{a}}\).

Answer:

\(2\sqrt{a}\cos a\)

Question. 25

Evaluate \(\displaystyle\lim_{x\to\tfrac{\pi}{6}}\dfrac{\cot^{2}x-3}{\cosec x-2}\).

Answer:

4

Question. 26

Evaluate \(\displaystyle\lim_{x\to0}\dfrac{\sqrt{2}-\sqrt{1+\cos x}}{\sin^{2}x}\).

Answer:

\(\dfrac{1}{4\sqrt{2}}\)

Question. 27

Evaluate \(\displaystyle\lim_{x\to0}\dfrac{\sin x-2\sin3x+\sin5x}{x}\).

Answer:

0

Question. 28

If \(\displaystyle\lim_{x\to1}\dfrac{x^{4}-1}{x-1}=\lim_{x\to k}\dfrac{x^{3}-k^{3}}{x^{2}-k^{2}}\), then find \(k\).

Answer:

\(k=\dfrac{3}{8}\)

Question. 29

Differentiate with respect to \(x\): \(\displaystyle f(x)=\dfrac{x^{4}+x^{3}+x^{2}+1}{x}\).

Answer:

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

Question. 30

Differentiate with respect to \(x\): \(\displaystyle f(x)=\left(x+\dfrac{1}{x}\right)^{3}\).

Answer:

\(3\left(x+\dfrac{1}{x}\right)^{2}\left(1-\dfrac{1}{x^{2}}\right)\)

Question. 31

Differentiate with respect to \(x\): \(\displaystyle f(x)=(3x+5)(1+\tan x)\).

Answer:

\(3(1+\tan x)+(3x+5)\sec^{2}x\)

Question. 32

Differentiate with respect to \(x\): \(\displaystyle f(x)=(\sec x-1)(\sec x+1)=\sec^{2}x-1\).

Answer:

\(2\sec^{2}x\tan x\)

Question. 33

Differentiate with respect to \(x\): \(\displaystyle f(x)=\dfrac{3x+4}{5x^{2}-7x+9}\).

Answer:

\(\dfrac{55-40x-15x^{2}}{(5x^{2}-7x+9)^{2}}\)

Question. 34

Differentiate with respect to \(x\): \(\displaystyle f(x)=\dfrac{x^{5}-\cos x}{\sin x}\).

Answer:

\(\dfrac{(5x^{4}+\sin x)\sin x-(x^{5}-\cos x)\cos x}{\sin^{2}x}\)

Question. 35

Differentiate with respect to \(x\): \(\displaystyle f(x)=\dfrac{x^{2}\cos\tfrac{\pi}{4}}{\sin x}\) (note \(\cos\tfrac{\pi}{4}=\tfrac{1}{\sqrt{2}}\)).

Answer:

\(\dfrac{\sqrt{2}\,x\sin x- x^{2}\cos x}{2\sin^{2}x}\) (equivalently, compute using quotient rule with constant \(\cos\tfrac{\pi}{4}\))

Question. 36

Differentiate with respect to \(x\): \(\displaystyle f(x)=(ax^{2}+\cot x)(p+q\cos x)\).

Answer:

\( (2ax-\csc^{2}x)(p+q\cos x)+(ax^{2}+\cot x)(-q\sin x)\)

Question. 37

Differentiate with respect to \(x\): \(\displaystyle f(x)=\dfrac{a+b\sin x}{c+d\cos x}\).

Answer:

\(\dfrac{(b\cos x)(c+d\cos x)-(a+b\sin x)(-d\sin x)}{(c+d\cos x)^{2}}\)

Question. 38

Differentiate with respect to \(x\): \(\displaystyle f(x)=(\sin x+\cos x)^{2}\).

Answer:

\(2(\sin x+\cos x)(\cos x-\sin x)\)

Question. 39

Differentiate with respect to \(x\): \(\displaystyle f(x)=(2x-7)^{2}(3x+5)^{3}\).

Answer:

Use product rule: \(2(2x-7)(2)(3x+5)^{3}+(2x-7)^{2}\cdot3(3x+5)^{2}\cdot3\).

Question. 40

Differentiate with respect to \(x\): \(\displaystyle f(x)=x^{2}\sin x+2x\sin x-2\sin2x\).

Answer:

\(2x\sin x+x^{2}\cos x+2\sin x+2x\cos x-4\cos2x\)

Question. 41

Differentiate with respect to \(x\): \(\displaystyle f(x)=\sin^{3}x\cos^{3}x\).

Answer:

\(3\sin^{2}x\cos^{3}x\cos x+3\sin^{3}x\cos^{2}x(-\sin x)\) (apply product rule or write \( (\sin x\cos x)^{3}\)).

Question. 42

Differentiate with respect to \(x\): \(\displaystyle f(x)=\dfrac{1}{ax^{2}+bx+c}\).

Answer:

\(-\dfrac{2ax+b}{(ax^{2}+bx+c)^{2}}\)

Long Answer Questions

Question. 43

Differentiate with respect to x: \(\cos\big(x^{2}+1\big)\).

Answer:

\(-2x\sin\big(x^{2}+1\big)\)

Question. 44

Differentiate with respect to x: \(\dfrac{ax+b}{cx+d}\).

Answer:

\(\dfrac{ad-bc}{(cx+d)^{2}}\)

Question. 45

Differentiate with respect to x: \(x^{2/3}\).

Answer:

\(\dfrac{2}{3}x^{-1/3}\)

Question. 46

Differentiate with respect to x: \(x\cos x\).

Answer:

\(\cos x - x\sin x\)

Question. 47

Evaluate: \(\displaystyle \lim_{y\to 0} \dfrac{(x+y)\sec(x+y)-x\sec x}{y}\).

Answer:

\(\sec x\big(x\tan x+1\big)\)

Question. 48

Evaluate: \(\displaystyle \lim_{x\to 0} \dfrac{\sin(\alpha+\beta)x+\sin(\alpha-\beta)x+\sin 2\alpha x}{\cos 2\beta x-\cos 2\alpha x}\cdot x\).

Answer:

\(\dfrac{2\alpha}{\alpha^{2}-\beta^{2}}\)

Question. 49

Evaluate: \(\displaystyle \lim_{x\to \tfrac{\pi}{4}} \dfrac{\tan^{3}x-\tan x}{\cos\big(x+\tfrac{\pi}{4}\big)}\).

Answer:

-4

Question. 50

Evaluate: \(\displaystyle \lim_{x\to\pi} \dfrac{1-\sin\tfrac{x}{2}}{\cos\tfrac{x}{2}\big(\cos\tfrac{x}{4}-\sin\tfrac{x}{4}\big)}\).

Answer:

\(\dfrac{1}{\sqrt{2}}\)

Question. 51

Evaluate (show whether limit exists): \(\displaystyle \lim_{x\to 4} \dfrac{|x-4|}{x-4}\).

Answer:

Does not exist

Question. 52

Evaluate (find constant): Let \(f(x)=\begin{cases}\dfrac{k\cos x}{\pi-2x}&\text{when }x\neq\dfrac{\pi}{2},\\[6pt]3&\text{when }x=\dfrac{\pi}{2}.\end{cases}\) If \(\displaystyle\lim_{x\to\tfrac{\pi}{2}} f(x)=f\big(\tfrac{\pi}{2}\big)\), find \(k\).

Answer:

\(6\)

Question. 53

Evaluate (find constant): Let \(f(x)=\begin{cases}x+2,&x\le 1,\\[6pt]cx^{2},&x>-1.\end{cases}\) Find \(c\) if \(\displaystyle\lim_{x\to -1} f(x)\) exists.

Answer:

\(1\)

Objective Type Question

Choose the correct answer from the given four options:

Question.  54

\(\lim_{x\to\pi} \dfrac{\sin x}{x-\pi}\) is

(A)

1

(B)

2

(C)

-1

(D)

-2

Question.  55

\(\lim_{x\to 0} \dfrac{x^{2}\cos x}{1-\cos x}\) is

(A)

2

(B)

\(\tfrac{3}{2}\)

(C)

\(-\tfrac{3}{2}\)

(D)

1

Question.  56

\(\lim_{x\to 0} \dfrac{(1+x)^{n}-1}{x}\) is

(A)

\(n\)

(B)

1

(C)

\(-n\)

(D)

0

Question.  57

\(\lim_{x\to 1} \dfrac{x^{m}-1}{x^{n}-1}\) is

(A)

1

(B)

\(\dfrac{m}{n}\)

(C)

\(-\dfrac{m}{n}\)

(D)

\(\dfrac{m^{2}}{n^{2}}\)

Question.  58

\(\lim_{\theta\to 0} \dfrac{1-\cos 4\theta}{1-\cos 6\theta}\) is

(A)

\(\dfrac{4}{9}\)

(B)

\(\dfrac{1}{2}\)

(C)

\(-\dfrac{1}{2}\)

(D)

-1

Question.  59

\(\lim_{x\to 0} \dfrac{\csc x - \cot x}{x}\) is

(A)

\(-\tfrac{1}{2}\)

(B)

1

(C)

\(\tfrac{1}{2}\)

(D)

1

Question.  60

\(\lim_{x\to 0} \dfrac{\sin x}{\sqrt{x+1}-\sqrt{1-x}}\) is

(A)

2

(B)

0

(C)

1

(D)

-1

Question.  61

\(\lim_{x\to \dfrac{\pi}{4}} \dfrac{\sec^{2}x -2}{\tan x -1}\) is

(A)

3

(B)

1

(C)

0

(D)

\(\sqrt{2}\)

Question.  62

\(\lim_{x\to 1} \dfrac{(\sqrt{x}-1)(2x-3)}{2x^{2}+x-3}\) is

(A)

\(\dfrac{1}{10}\)

(B)

\(-\dfrac{1}{10}\)

(C)

1

(D)

None of these

Question.  63

Let \(f(x)=\begin{cases}\dfrac{\sin[ x ]}{[ x ]},&[ x ]\ne 0\\0,&[ x ]=0\end{cases}\) where \([\cdot]\) denotes the greatest integer function. Then \(\lim_{x\to 0} f(x)\) is

(A)

1

(B)

0

(C)

-1

(D)

None of these

Question.  64

\(\lim_{x\to 0} \dfrac{|\sin x|}{x}\) is

(A)

1

(B)

-1

(C)

does not exist

(D)

None of these

Question.  65

Let \(f(x)=\begin{cases}x^{2}-1,&0

(A)

\(x^{2}-6x+9=0\)

(B)

\(x^{2}-7x+8=0\)

(C)

\(x^{2}-14x+49=0\)

(D)

\(x^{2}-10x+21=0\)

Question.  66

\(\lim_{x\to 0} \dfrac{\tan 2x - x}{3x - \sin x}\)

(A)

2

(B)

\(\dfrac{1}{2}\)

(C)

\(-\dfrac{1}{2}\)

(D)

\(\dfrac{1}{4}\)

Question.  67

Let \(f(x)=x-[x]\), \(x\in\mathbb{R}\). Then \(f'(\tfrac{1}{2})\) is

(A)

\(\dfrac{3}{2}\)

(B)

1

(C)

0

(D)

-1

Question.  68

If \(y=\sqrt{x}+\dfrac{1}{\sqrt{x}}\), then \(\dfrac{dy}{dx}\) at \(x=1\) is

(A)

1

(B)

\(\dfrac{1}{2}\)

(C)

\(\dfrac{1}{\sqrt{2}}\)

(D)

0

Question.  69

If \(f(x)=\dfrac{x-4}{2\sqrt{x}}\), then \(f'(1)\) is

(A)

\(\dfrac{5}{4}\)

(B)

\(\dfrac{4}{5}\)

(C)

1

(D)

0

Question.  70

If \(y=\dfrac{1+\dfrac{1}{x^{2}}}{1-\dfrac{1}{x^{2}}}\), then \(\dfrac{dy}{dx}\) is

(A)

\(-\dfrac{4x}{(x^{2}-1)^{2}}\)

(B)

\(-\dfrac{4x}{x^{2}-1}\)

(C)

\(\dfrac{1-x^{2}}{4x}\)

(D)

\(\dfrac{4x}{x^{2}-1}\)

Question.  71

If \(y=\dfrac{\sin x+\cos x}{\sin x-\cos x}\), then \(\dfrac{dy}{dx}\) at \(x=0\) is

(A)

-2

(B)

0

(C)

\(\dfrac{1}{2}\)

(D)

does not exist

Question.  72

If \(y=\dfrac{\sin(x+9)}{\cos x}\), then \(\dfrac{dy}{dx}\) at \(x=0\) is

(A)

\(\cos 9\)

(B)

\(\sin 9\)

(C)

0

(D)

1

Question.  73

If \(f(x)=1+x+\dfrac{x^{2}}{2}+\dots+\dfrac{x^{100}}{100}\), then \(f'(1)\) is equal to

(A)

\(\dfrac{1}{100}\)

(B)

100

(C)

does not exist

(D)

0

Question.  74

If \(f(x)=\dfrac{x^{n}-a^{n}}{x-a}\) for some constant \(a\), then \(f'(a)\) is

(A)

1

(B)

0

(C)

does not exist

(D)

\(\dfrac{1}{2}\)

Question.  75

If \(f(x)=x^{100}+x^{99}+\dots+x+1\), then \(f'(1)\) is equal to

(A)

5050

(B)

5049

(C)

5051

(D)

50051

Question.  76

If \(f(x)=1-x+x^{2}-x^{3}+\dots+ x^{100}\), then \(f'(1)\) is equal to

(A)

150

(B)

-50

(C)

-150

(D)

50

Fill in the Blanks

Question. 77

If \( f(x) = \dfrac{\tan x}{x - \pi} \), then \( \lim_{x \to \pi} f(x) = \_\_\_\_\_\_\_\_\_\_ \)

Answer:

1

Question. 78

\( \lim_{x \to 0} \left( \sin(mx) \cot \dfrac{x}{\sqrt{3}} \right) = 2 \), then \( m = \_\_\_\_\_\_\_\_ \)

Answer:

\( \dfrac{2\sqrt{3}}{3} \)

Question. 79

If \( y = 1 + \dfrac{x}{1!} + \dfrac{x^{2}}{2!} + \dfrac{x^{3}}{3!} + \ldots \), then \( \dfrac{dy}{dx} = \_\_\_\_\_\_\_\_ \)

Answer:

y

Question. 80

\( \lim_{x \to 3^{+}} \dfrac{x}{[x]} = \_\_\_\_\_\_\_ \)

Answer:

1

NCERT Exemplar Solutions Class 11 – Mathematics – Chapter 13: LIMITS AND DERIVATIVES | Detailed Answers