NCERT Exemplar Solutions
Class 12 - Mathematics
Chapter 2: INVERSE TRIGONOMETRIC FUNCTIONS

Inverse function, Graph of an inverse trigonometric function, Properties of inverse trigonometric functions.

Short Answer (S.A.)

Question. 1

Find the value of \( \tan^{-1}(\tan 5\pi/6) + \cos^{-1}(\cos 13\pi/6) \).

Answer:

0

Question. 2

Evaluate \( \cos[\cos^{-1}(-\sqrt{3}/2) + \pi/6] \).

Answer:

-1

Question. 3

Prove that \( \cot(\pi/4 - 2\cot^{-1}3) = 7 \).

Answer:

7

Question. 4

Find the value of \( \tan^{-1}(-1/\sqrt{3}) + \cot^{-1}(1/\sqrt{3}) + \tan^{-1}(\sin(-\pi/2)) \).

Answer:

-\pi/12

Question. 5

Find the value of \( \tan^{-1}(\tan 2\pi/3) \).

Answer:

-\pi/3

Question. 6

Show that \( 2\tan^{-1}(-3) = -\pi/2 + \tan^{-1}(-4/3) \).

Answer:

-\pi/2 + \tan^{-1}(-4/3)

Question. 7

Find the real solutions of the equation \( \tan^{-1}\sqrt{x(x+1)} + \sin^{-1}\sqrt{x^{2}+x+1} = \pi/2 \).

Answer:

0, -1

Question. 8

Find the value of the expression \( \sin(2\tan^{-1}(1/3)) + \cos(\tan^{-1}(2\sqrt{2})) \).

Answer:

14/15

Question. 9

If \( 2\tan^{-1}(\cos \theta) = \tan^{-1}(2\csc \theta) \), then show that \( \theta = \pi/4 \).

Answer:

\pi/4

Question. 10

Show that \( \cos(2\tan^{-1}(1/7)) = \sin(4\tan^{-1}(1/3)) \).

Answer:

Both sides are equal.

Question. 11

Solve the equation \( \cos(\tan^{-1} x) = \sin(\cot^{-1}(3/4)) \).

Answer:

-3/4, 3/4

Long Answer Questions

Question. 12

Prove that \(\tan^{-1}\left(\dfrac{\sqrt{1+x^{2}} + \sqrt{1-x^{2}}}{\sqrt{1+x^{2}} - \sqrt{1-x^{2}}}\right) = \dfrac{\pi}{4} + \dfrac{1}{2} \cos^{-1} x^{2}\).

Question. 13

Find the simplified form of \(\cos^{-1}\left(\dfrac{3}{5}\cos x + \dfrac{4}{5}\sin x\right)\), where \(x \in \left[ -\dfrac{3\pi}{4}, \dfrac{\pi}{4} \right]\).

Answer:

\(\tan^{-1}\dfrac{4}{3} - x\)

Question. 14

Prove that \(\sin^{-1}\dfrac{8}{17} + \sin^{-1}\dfrac{3}{5} = \sin^{-1}\dfrac{77}{85}\).

Answer:

\(\dfrac{77}{85}\)

Question. 15

Show that \(\sin^{-1}\dfrac{5}{13} + \cos^{-1}\dfrac{3}{5} = \tan^{-1}\dfrac{63}{16}\).

Answer:

\(\dfrac{63}{16}\)

Question. 16

Prove that \(\tan^{-1}\dfrac{1}{4} + \tan^{-1}\dfrac{2}{9} = \sin^{-1}\dfrac{1}{\sqrt{5}}\).

Answer:

\(\dfrac{1}{\sqrt{5}}\)

Question. 17

Find the value of \(4 \tan^{-1}\dfrac{1}{5} - \tan^{-1}\dfrac{1}{239}\).

Answer:

\(\dfrac{\pi}{4}\)

Question. 18

Show that \(\tan\left(\dfrac{1}{2}\sin^{-1}\dfrac{3}{4}\right) = \dfrac{4 - \sqrt{7}}{3}\) and justify why the other value \(\dfrac{4 + \sqrt{7}}{3}\) is ignored.

Answer:

\(\dfrac{4 - \sqrt{7}}{3}\)

Question. 19

If \(a_{1}, a_{2}, a_{3}, \ldots, a_{n}\) is an arithmetic progression with common difference \(d\), evaluate the expression:

\[ \tan \left[ \tan^{-1}\left(\dfrac{d}{1 + a_{1}a_{2}}\right) + \tan^{-1}\left(\dfrac{d}{1 + a_{2}a_{3}}\right) + \tan^{-1}\left(\dfrac{d}{1 + a_{3}a_{4}}\right) + \cdots + \tan^{-1}\left(\dfrac{d}{1 + a_{n-1}a_{n}}\right) \right] \]

Answer:

\(\dfrac{a_{n} - a_{1}}{1 + a_{1}a_{n}}\)

Objective Type Question

Choose the correct answer from the given four options:

Question.  20

Which of the following is the principal value branch of \(\cos^{-1} x\)?

(a)

\([-\dfrac{\pi}{2}, \dfrac{\pi}{2}]\)

(b)

(0, \pi)

(c)

[0, \pi]

(d)

(0, \dfrac{\pi}{2}]

Question.  21

Which of the following is the principal value branch of \(\csc^{-1} x\)?

(a)

\((-\dfrac{\pi}{2}, -\dfrac{\pi}{2})\)

(b)

[0, \pi] - \{\dfrac{\pi}{2}\}

(c)

\([-\dfrac{\pi}{2}, \dfrac{\pi}{2}]\)

(d)

\([-\dfrac{\pi}{2}, \dfrac{\pi}{2}] - \{0\}\)

Question.  22

If \(3 \tan^{-1} x + \cot^{-1} x = \pi\), then \(x\) equals

(a)

0

(b)

1

(c)

-1

(d)

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

Question.  23

The value of \(\sin^{-1}\left(\cos \dfrac{33\pi}{5}\right)\) is

(a)

\(\dfrac{3\pi}{5}\)

(b)

\(-\dfrac{7\pi}{5}\)

(c)

\(\dfrac{\pi}{10}\)

(d)

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

Question.  24

The domain of the function \(\cos^{-1}(2x - 1)\) is

(a)

[0, 1]

(b)

[-1, 1]

(c)

(-1, 1)

(d)

[0, \pi]

Question.  25

The domain of the function defined by \(f(x) = \sin^{-1} \sqrt{x - 1}\) is

(a)

[1, 2]

(b)

[-1, 1]

(c)

[0, 1]

(d)

none of these

Question.  26

If \(\cos\left(\sin^{-1} \dfrac{2}{5} + \cos^{-1} x\right) = 0\), then \(x\) is equal to

(a)

\(\dfrac{1}{5}\)

(b)

\(\dfrac{2}{5}\)

(c)

0

(d)

1

Question.  27

The value of \(\sin(2 \tan^{-1}(0.75))\) is equal to

(a)

.75

(b)

1.5

(c)

.96

(d)

\(\sin^{-1} 5\)

Question.  28

The value of \(\cos^{-1}(\cos \dfrac{3\pi}{2})\) is equal to

(a)

\(\dfrac{\pi}{2}\)

(b)

\(3\pi\)

(c)

\(\dfrac{5\pi}{2}\)

(d)

\(7\pi\)

Question.  29

The value of the expression \(2 \sec^{-1} 2 + \sin^{-1} \left(\dfrac{1}{2}\right)\) is

(a)

\(\dfrac{\pi}{6}\)

(b)

\(\dfrac{5\pi}{6}\)

(c)

\(\dfrac{7\pi}{6}\)

(d)

1

Question.  30

If \(\tan^{-1} x + \tan^{-1} y = \dfrac{4\pi}{5}\), then \(\cot^{-1} x + \cot^{-1} y\) equals

(a)

\(\dfrac{\pi}{5}\)

(b)

\(\dfrac{2\pi}{5}\)

(c)

\(\dfrac{3\pi}{5}\)

(d)

\(\pi\)

Question.  31

If \(\sin^{-1}\left(\dfrac{2a}{1 + a^{2}}\right) + \cos^{-1}\left(\dfrac{1 - a^{2}}{1 + a^{2}}\right) = \tan^{-1}\left(\dfrac{2x}{1 - x^{2}}\right)\), where \(a, x \in (0, 1)\), then the value of \(x\) is

(a)

0

(b)

\(\dfrac{a}{2}\)

(c)

a

(d)

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

Question.  32

The value of \(\cot \left[ \cos^{-1} \left(\dfrac{7}{25}\right) \right]\) is

(a)

\(\dfrac{25}{24}\)

(b)

\(\dfrac{25}{7}\)

(c)

\(\dfrac{24}{25}\)

(d)

\(\dfrac{7}{24}\)

Question.  33

The value of the expression \(\tan\left(\dfrac{1}{2} \cos^{-1} \dfrac{2}{\sqrt{5}}\right)\) is

(a)

\(2 + \sqrt{5}\)

(b)

\(\sqrt{5} - 2\)

(c)

\(\dfrac{\sqrt{5} + 2}{2}\)

(d)

5 + \sqrt{2}

Question.  34

If \(x \le 1\), then \(2 \tan^{-1} x + \sin^{-1}\left(\dfrac{2x}{1 + x^{2}}\right)\) is equal to

(a)

\(4 \tan^{-1} x\)

(b)

0

(c)

\(\dfrac{\pi}{2}\)

(d)

\(\pi\)

Question.  35

If \(\cos^{-1} \alpha + \cos^{-1} \beta + \cos^{-1} \gamma = 3\pi\), then \(\alpha(\beta + \gamma) + \beta(\gamma + \alpha) + \gamma(\alpha + \beta)\) equals

(a)

0

(b)

1

(c)

6

(d)

12

Question.  36

The number of real solutions of the equation \(\sqrt{1 + \cos 2x} = \sqrt{2} \cos^{-1}(\cos x)\) in \([\dfrac{\pi}{2}, \pi]\) is

(a)

0

(b)

1

(c)

2

(d)

Infinite

Question.  37

If \(\cos^{-1} x > \sin^{-1} x\), then

(a)

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

(b)

0 \le x < \dfrac{1}{\sqrt{2}}\)

(c)

-1 \le x < \dfrac{1}{\sqrt{2}}\)

(d)

x > 0

Fill in the Blanks

Question. 38

The principal value of \(\cos^{-1}(-\dfrac{1}{2})\) is ____.

Answer:

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

Question. 39

The value of \(\sin^{-1}\left(\sin \dfrac{3\pi}{5}\right)\) is ____.

Answer:

\(\dfrac{2\pi}{5}\)

Question. 40

If \(\cos(\tan^{-1} x + \cot^{-1} \sqrt{3}) = 0\), then value of \(x\) is ____.

Answer:

\(\sqrt{3}\)

Question. 41

The set of values of \(\sec^{-1}\left(\dfrac{1}{2}\right)\) is ____.

Answer:

\(\varphi\)

Question. 42

The principal value of \(\tan^{-1} \sqrt{3}\) is ____.

Answer:

\(\dfrac{\pi}{3}\)

Question. 43

The value of \(\cos^{-1}(\cos \dfrac{14\pi}{3})\) is ____.

Answer:

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

Question. 44

The value of \(\cos(\sin^{-1} x + \cos^{-1} x)\), \(|x| \le 1\), is ____.

Answer:

0

Question. 45

The value of the expression \(\tan\left(\dfrac{\sin^{-1} x + \cos^{-1} x}{2}\right)\), when \(x = \dfrac{\sqrt{3}}{2}\), is ____.

Answer:

1

Question. 46

If \(y = 2 \tan^{-1} x + \sin^{-1}\left(\dfrac{2x}{1 + x^{2}}\right)\) for all \(x\), then ____ < y < ____.

Answer:

-2\pi

2\pi

Question. 47

The result \(\tan^{-1} x - \tan^{-1} y = \tan^{-1}\left(\dfrac{x - y}{1 + xy}\right)\) is true when value of \(xy\) is ____.

Answer:

\(xy > -1\)

Question. 48

The value of \(\cot^{-1}(-x)\) for all \(x \in \mathbb{R}\) in terms of \(\cot^{-1} x\) is ____.

Answer:

\(\pi - \cot^{-1} x\)

True or False

Question. 49

All trigonometric functions have inverse over their respective domains.

Answer:

False

Question. 50

The value of the expression \((\cos^{-1} x)^2\) is equal to \(\sec^{2} x\).

Answer:

False

Question. 51

The domain of trigonometric functions can be restricted to any one of their branches (not necessarily principal value) in order to obtain their inverse functions.

Answer:

True

Question. 52

The least numerical value, either positive or negative, of angle \(\theta\) is called the principal value of the inverse trigonometric function.

Answer:

True

Question. 53

The graph of an inverse trigonometric function can be obtained from the graph of its corresponding trigonometric function by interchanging \(x\) and \(y\) axes.

Answer:

True

Question. 54

The minimum value of \(n\) for which \(\tan^{-1} \dfrac{n}{\pi} = \dfrac{\pi}{4}\), \(n \in \mathbb{N}\), is valid is 5.

Answer:

False

Question. 55

The principal value of \(\sin^{-1}\left[\cos\left(\sin^{-1} \dfrac{1}{2}\right)\right]\) is \(\dfrac{\pi}{3}\).

Answer:

True

NCERT Exemplar Solutions Class 12 – Mathematics – Chapter 2: INVERSE TRIGONOMETRIC FUNCTIONS | Detailed Answers