NCERT Exemplar Solutions
Class 11 - Mathematics
Chapter 3: TRIGONOMETRIC FUNCTIONS

Relation between degree and radian, Trigonometric functions, Trigonometric equations

Short Answer Type

Question. 1

Prove that \(\dfrac{\tan A + \sec A - 1}{\tan A - \sec A + 1} = \dfrac{1 + \sin A}{\cos A}\).

Question. 2

If \(\dfrac{2\sin\alpha}{1 + \cos\alpha + \sin\alpha} = y\), then prove that \(\dfrac{1 - \cos\alpha + \sin\alpha}{1 + \sin\alpha}\) is also equal to \(y\).

Question. 3

If \(m\sin\theta = n\sin(\theta + 2\alpha)\), then prove that \(\tan(\theta + \alpha)\cot\alpha = \dfrac{m + n}{m - n}\).

Question. 4

If \(\cos(\alpha + \beta) = \dfrac{4}{5}\) and \(\sin(\alpha - \beta) = \dfrac{5}{13}\), where \(\alpha\) lies between \(0\) and \(\dfrac{\pi}{4}\), find the value of \(\tan 2\alpha\).

Question. 5

If \(\tan x = \dfrac{b}{a}\), then find the value of \(\sqrt{\dfrac{a + b}{a - b}} + \sqrt{\dfrac{a - b}{a + b}}\).

Question. 6

Prove that \(\cos\theta\cos\dfrac{\theta}{2} - \cos3\theta\cos\dfrac{9\theta}{2} = \sin7\theta\sin8\theta\).

Question. 7

If \(a\cos\theta + b\sin\theta = m\) and \(a\sin\theta - b\cos\theta = n\), then show that \(a^2 + b^2 = m^2 + n^2\).

Question. 8

Find the value of \(\tan 22^{\circ}30'\).

Question. 9

Prove that \(\sin 4A = 4\sin A\cos^{3}A - 4\cos A\sin^{3}A\).

Question. 10

If \(\tan\theta + \sin\theta = m\) and \(\tan\theta - \sin\theta = n\), then prove that \(m^2 - n^2 = 4\sin\theta\tan\theta\).

Question. 11

If \(\tan(A + B) = p\) and \(\tan(A - B) = q\), then show that \(\tan 2A = \dfrac{p + q}{1 - pq}\).

Question. 12

If \(\cos\alpha + \cos\beta = 0 = \sin\alpha + \sin\beta\), then prove that \(\cos 2\alpha + \cos 2\beta = -2\cos(\alpha + \beta)\).

Question. 13

If \(\dfrac{\sin(x + y)}{\sin(x - y)} = \dfrac{a + b}{a - b}\), then show that \(\dfrac{\tan x}{\tan y} = \dfrac{a}{b}\).

Question. 14

If \(\tan\theta = \dfrac{\sin\alpha - \cos\alpha}{\sin\alpha + \cos\alpha}\), then show that \(\sin\alpha + \cos\alpha = \sqrt{2}\cos\theta\).

Question. 15

If \(\sin\theta + \cos\theta = 1\), then find the general value of \(\theta\).

Question. 16

Find the most general value of \(\theta\) satisfying the equations \(\tan\theta = -1\) and \(\cos\theta = \dfrac{1}{\sqrt{2}}\).

Question. 17

If \(\cot\theta + \tan\theta = 2\csc\theta\), then find the general value of \(\theta\).

Question. 18

If \(2\sin^{2}\theta = 3\cos\theta\), where \(0 \le \theta \le 2\pi\), then find the value(s) of \(\theta\).

Question. 19

If \(\sec x \cos 5x + 1 = 0\), where \(0 < x \le \dfrac{\pi}{2}\), then find the value of \(x\).

Long Answer Type

Question. 20

If \(\sin(\theta + \alpha) = a\) and \(\sin(\theta + \beta) = b\), then prove that \(\cos 2(\alpha - \beta) - 4ab \cos(\alpha - \beta) = 1 - 2a^2 - 2b^2\).

Question. 21

If \(\cos(\theta + \phi) = m \cos(\theta - \phi)\), then prove that \(\tan \theta = \dfrac{1 - m}{1 + m} \cot \phi\).

Question. 22

Find the value of the expression

\(3\left[\sin^4\left(\dfrac{3\pi}{2} - \alpha\right) + \sin^4(3\pi + \alpha)\right] - 2\left[\sin^6\left(\dfrac{\pi}{2} + \alpha\right) + \sin^6(5\pi - \alpha)\right].\)

Answer:

1

Question. 23

If an equation \(a \cos 2\theta + b \sin 2\theta = c\) has \(\alpha\) and \(\beta\) as its roots, then prove that

\(\tan \alpha + \tan \beta = \dfrac{2b}{a + c}.\)

Question. 24

If \(x = \sec \phi - \tan \phi\) and \(y = \csc \phi + \cot \phi\), then show that \(xy + x - y + 1 = 0\).

Question. 25

If \(\theta\) lies in the first quadrant and \(\cos \theta = \dfrac{8}{17}\), then find the value of

\(\cos(30^{\circ} + \theta) + \cos(45^{\circ} - \theta) + \cos(120^{\circ} - \theta).\)

Answer:

\(\dfrac{23}{17}\left(\dfrac{\sqrt{3} - 1}{2} + \dfrac{1}{\sqrt{2}}\right)\)

Question. 26

Find the value of the expression

\(\cos^4\dfrac{\pi}{8} + \cos^4\dfrac{3\pi}{8} + \cos^4\dfrac{5\pi}{8} + \cos^4\dfrac{7\pi}{8}.\)

Answer:

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

Question. 27

Find the general solution of the equation \(5\cos^2\theta + 7\sin^2\theta - 6 = 0\).

Answer:

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

Question. 28

Find the general solution of the equation

\(\sin x - 3 \sin 2x + \sin 3x = \cos x - 3 \cos 2x + \cos 3x.\)

Answer:

\(\dfrac{n\pi}{2} \pm \dfrac{\pi}{8}\)

Question. 29

Find the general solution of the equation

\((\sqrt{3} - 1)\cos \theta + (\sqrt{3} + 1)\sin \theta = 2.\)

Answer:

\(\theta = 2n\pi \pm \dfrac{\pi}{4} + \dfrac{\pi}{12}\)

Objective Type Questions

Choose the correct answer from the given four options:

Question.  30

If \(\sin\theta + \csc\theta = 2\), then \(\sin^2\theta + \csc^2\theta\) is equal to

(a)

1

(b)

4

(c)

2

(d)

None of these

Question.  31

If \(f(x)=\cos^2 x + \sec^2 x\), then

(a)

\(f(x) < 1\)

(b)

\(f(x)=1\)

(c)

\(2 < f(x) < 1\)

(d)

\(f(x) \ge 2\)

Question.  32

If \(\tan\theta=\dfrac{1}{2}\) and \(\tan\phi=\dfrac{1}{3}\), then the value of \(\theta+\phi\) is

(a)

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

(b)

\(\pi\)

(c)

0

(d)

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

Question.  33

Which of the following is not correct?

(a)

\(\sin\theta = -\dfrac{1}{5}\)

(b)

\(\cos\theta = 1\)

(c)

\(\sec\theta = \dfrac{1}{2}\)

(d)

\(\tan\theta = 20\)

Question.  34

The value of \(\tan1^\circ\tan2^\circ\tan3^\circ\dots\tan89^\circ\) is

(a)

0

(b)

1

(c)

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

(d)

Not defined

Question.  35

The value of \(\dfrac{1-\tan^2 15^\circ}{1+\tan^2 15^\circ}\) is

(a)

1

(b)

\(\sqrt{3}\)

(c)

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

(d)

2

Question.  36

The value of \(\cos1^\circ\cos2^\circ\cos3^\circ\dots\cos179^\circ\) is

(a)

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

(b)

0

(c)

1

(d)

-1

Question.  37

If \(\tan\theta=3\) and \(\theta\) lies in the third quadrant, then the value of \(\sin\theta\) is

(a)

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

(b)

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

(c)

\(-\dfrac{3}{\sqrt{10}}\)

(d)

\(\dfrac{3}{\sqrt{10}}\)

Question.  38

The value of \(\tan75^\circ - \cot75^\circ\) is equal to

(a)

\(2\sqrt{3}\)

(b)

2 + \(\sqrt{3}\)

(c)

2 - \(\sqrt{3}\)

(d)

1

Question.  39

Which of the following is correct?

(a)

\(\sin1^\circ > \sin1\)

(b)

\(\sin1^\circ < \sin1\)

(c)

\(\sin1^\circ = \sin1\)

(d)

\(\sin1^\circ = \dfrac{\pi}{18}\sin1\)

Question.  40

If \(\tan\alpha=\dfrac{m}{m+1}\), \(\tan\beta=\dfrac{1}{2m+1}\), then \(\alpha+\beta\) is equal to

(a)

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

(b)

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

(c)

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

(d)

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

Question.  41

The minimum value of \(3\cos x + 4\sin x + 8\) is

(a)

5

(b)

9

(c)

7

(d)

3

Question.  42

The value of \(\tan3A - \tan2A - \tan A\) is equal to

(a)

\(\tan3A\tan2A\tan A\)

(b)

\(-\tan3A\tan2A\tan A\)

(c)

\(\tan A\tan2A - \tan2A\tan3A - \tan3A\tan A\)

(d)

None of these

Question.  43

The value of \(\sin(45^\circ + \theta) - \cos(45^\circ - \theta)\) is

(a)

\(2\cos\theta\)

(b)

\(2\sin\theta\)

(c)

1

(d)

0

Question.  44

The value of \(\cot\left(\dfrac{\pi}{4}+\theta\right)\cot\left(\dfrac{\pi}{4}-\theta\right)\) is

(a)

-1

(b)

0

(c)

1

(d)

Not defined

Question.  45

\(\cos2\theta\cos2\phi + \sin^2(\theta-\phi) - \sin^2(\theta+\phi)\) is equal to

(a)

\(\sin2(\theta+\phi)\)

(b)

\(\cos2(\theta+\phi)\)

(c)

\(\sin2(\theta-\phi)\)

(d)

\(\cos2(\theta-\phi)\)

Question.  46

The value of \(\cos12^\circ + \cos84^\circ + \cos156^\circ + \cos132^\circ\) is

(a)

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

(b)

1

(c)

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

(d)

\(\dfrac{1}{8}\)

Question.  47

If \(\tan A=\dfrac{1}{2}\), \(\tan B=\dfrac{1}{3}\), then \(\tan(2A+B)\) is equal to

(a)

1

(b)

2

(c)

3

(d)

4

Question.  48

The value of \(\sin\dfrac{\pi}{10} - \sin\dfrac{13\pi}{10}\) is

(a)

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

(b)

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

(c)

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

(d)

1

Question.  49

The value of \(\sin50^\circ - \sin70^\circ + \sin10^\circ\) is equal to

(a)

1

(b)

0

(c)

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

(d)

2

Question.  50

If \(\sin\theta + \cos\theta = 1\), then the value of \(\sin2\theta\) is equal to

(a)

1

(b)

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

(c)

0

(d)

-1

Question.  51

If \(\alpha + \beta = \dfrac{\pi}{4}\), then the value of \((1+\tan\alpha)(1+\tan\beta)\) is

(a)

1

(b)

2

(c)

-2

(d)

Not defined

Question.  52

If \(\sin\theta = -\dfrac{4}{5}\) and \(\theta\) lies in the third quadrant, then the value of \(\cos\dfrac{\theta}{2}\) is

(a)

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

(b)

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

(c)

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

(d)

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

Question.  53

Number of solutions of the equation \(\tan x + \sec x = 2\cos x\) lying in the interval \([0,2\pi]\) is

(a)

0

(b)

1

(c)

2

(d)

3

Question.  54

The value of \(\sin\dfrac{\pi}{18} + \sin\dfrac{\pi}{9} + \sin\dfrac{2\pi}{9} + \sin\dfrac{5\pi}{18}\) is given by

(a)

\(\sin\dfrac{7\pi}{18} + \sin\dfrac{4\pi}{9}\)

(b)

1

(c)

\(\cos\dfrac{\pi}{6} + \cos\dfrac{3\pi}{7}\)

(d)

\(\cos\dfrac{\pi}{9} + \sin\dfrac{\pi}{9}\)

Question.  55

If \(A\) lies in the second quadrant and \(3\tan A + 4 = 0\), then the value of \(2\cot A - 5\cos A + \sin A\) is equal to

(a)

-\(\dfrac{53}{10}\)

(b)

\(\dfrac{23}{10}\)

(c)

\(\dfrac{37}{10}\)

(d)

\(\dfrac{7}{10}\)

Question.  56

The value of \(\cos^2 48^\circ - \sin^2 12^\circ\) is

(a)

\(\dfrac{\sqrt{5}+1}{8}\)

(b)

\(\dfrac{\sqrt{5}-1}{8}\)

(c)

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

(d)

\(\dfrac{\sqrt{5}+1}{2\sqrt{2}}\)

Question.  57

If \(\tan\alpha=\dfrac{1}{7}\), \(\tan\beta=\dfrac{1}{3}\), then \(\cos2\alpha\) is equal to

(a)

\(\sin2\beta\)

(b)

\(\sin4\beta\)

(c)

\(\sin3\beta\)

(d)

\(\cos2\beta\)

Question.  58

If \(\tan\theta=\dfrac{a}{b}\), then \(b\cos2\theta + a\sin2\theta\) is equal to

(a)

a

(b)

b

(c)

\(\dfrac{a}{b}\)

(d)

None

Question.  59

If for real values of \(x\), \(\cos\theta = x + \dfrac{1}{x}\), then

(a)

\(\theta\) is an acute angle

(b)

\(\theta\) is right angle

(c)

\(\theta\) is an obtuse angle

(d)

No value of \(\theta\) is possible

Fill in the blanks in Exercises 60 to 67 :

Question. 60

The value of \( \dfrac{\sin 50^\circ}{\sin 130^\circ} \) is ____.

Answer:

1

Question. 61

If \( k = \sin\left(\dfrac{\pi}{18}\right) \sin\left(\dfrac{5\pi}{18}\right) \sin\left(\dfrac{7\pi}{18}\right) \), then the numerical value of \( k \) is ____.

Answer:

\(\dfrac{1}{8}\)

Question. 62

If \( \tan A = \dfrac{1 - \cos B}{\sin B} \), then \( \tan 2A = ____ \).

Answer:

\(\tan \beta\)

Question. 63

If \(\sin x + \cos x = a\), then

(i) \( \sin^6 x + \cos^6 x = ____ \)

(ii) \(|\sin x - \cos x| = ____ \)

Answer:

\(\dfrac{1}{4}[4 - 3(a^2 - 1)^2]\), \(\sqrt{2 - a^2}\)

Question. 64

In a triangle ABC with \(\angle C = 90^\circ\) the equation whose roots are \(\tan A\) and \(\tan B\) is ____.

Answer:

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

Question. 65

\(3(\sin x - \cos x)^4 + 6(\sin x + \cos x)^2 + 4(\sin^6 x + \cos^6 x) = ____\).

Answer:

13

Question. 66

Given \(x > 0\), the values of \( f(x) = -3 \cos \sqrt{3 + x + x^2} \) lie in the interval ____.

Answer:

[ -3 , 3 ]

Question. 67

The maximum distance of a point on the graph of the function \( y = \sqrt{3} \sin x + \cos x \) from x-axis is ____.

Answer:

2

True or False

In each of the Exercises 68 to 75, state whether the statements is True or False? Also give justification.

Question. 68

If \( \, \tan A = \dfrac{1 - \cos B}{\sin B} \, \) then \( \, \tan 2A = \tan B \, \).

Answer:

True

Question. 69

The equality \( \, \sin A + \sin 2A + \sin 3A = 3 \, \) holds for some real value of \(A\).

Answer:

False

Question. 70

\( \, \sin 10^\circ \, \) is greater than \( \, \cos 10^\circ \, \).

Answer:

False

Question. 71

\( \cos \dfrac{2\pi}{15} \, \cos \dfrac{4\pi}{15} \, \cos \dfrac{8\pi}{15} \, \cos \dfrac{16\pi}{15} = \dfrac{1}{16} \).

Answer:

True

Question. 72

One value of \(\theta\) which satisfies the equation \( \, \sin^4 \theta - 2 \sin^2 \theta - 1 \, \) lies between \(0\) and \(2\pi\).

Answer:

False

Question. 73

If \( \, \csc x = 1 + \cot x \, \) then \( x = 2n\pi \) or \( x = 2n\pi + \dfrac{\pi}{2} \).

Answer:

True

Question. 74

If \( \, \tan \theta + \tan 2\theta + \sqrt{3} \, \tan \theta \, \tan 2\theta = \sqrt{3} \, \), then \( \, \theta = \dfrac{n\pi}{3} + \dfrac{\pi}{9} \, \).

Answer:

True

Question. 75

If \( \, \tan(\pi \cos \theta) = \cot(\pi \sin \theta) \, \) then \( \, \theta - \dfrac{\pi}{4} = \pm \dfrac{1}{2\sqrt{2}} \, \).

Answer:

True

Matching Question

Question. 76

Match the items in Column A with their corresponding expressions in Column B using the table below.

Column AColumn B

(a) \(\sin(x+y)\sin(x-y)\)

(i) \(\cos^2 x - \sin^2 y\)

(b) \(\cos(x+y)\cos(x-y)\)

(ii) \(\dfrac{1-\tan\theta}{1+\tan\theta}\)

(c) \(\cot\left(\dfrac{\pi}{4} + \theta\right)\)

(iii) \(\dfrac{1+\tan\theta}{1-\tan\theta}\)

(d) \(\tan\left(\dfrac{\pi}{4} + \theta\right)\)

(iv) \(\sin^2 x - \sin^2 y\)

Answer:

Column AMatched Item from Column B

(a) \(\sin(x+y)\sin(x-y)\)

(iv) \(\sin^2 x - \sin^2 y\)

(b) \(\cos(x+y)\cos(x-y)\)

(i) \(\cos^2 x - \sin^2 y\)

(c) \(\cot\left(\dfrac{\pi}{4} + \theta\right)\)

(ii) \(\dfrac{1-\tan\theta}{1+\tan\theta}\)

(d) \(\tan\left(\dfrac{\pi}{4} + \theta\right)\)

(iii) \(\dfrac{1+\tan\theta}{1-\tan\theta}\)

NCERT Exemplar Solutions Class 11 – Mathematics – Chapter 3: TRIGONOMETRIC FUNCTIONS | Detailed Answers