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

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

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