📏 Grade 10 Maths · Unit 6 · Samacheer Kalvi

Samacheer Class 10 Maths - Trigonometry

Free Content
All Book Back Q&A
10 Exercises
Step-by-Step Solutions

Complete step-by-step solutions for every exercise in Unit 6. Click any question to expand the full working.

Share on WhatsApp
📋 Exercises in this unit
Ex 6.1 — Trigonometric Identities Ex 6.1 — -- Ex 6.2 — Problems involving Angle of Elevation Ex 6.2 — -- Ex 6.3 — Problems involving Angle of Depression Ex 6.3 — -- Ex 6.4 — Problems involving Angle of Elevation and Depression Ex 6.4 — -- Ex 6.UE — Unit Exercise Ex 6.UE — Unit Exercise
Your Progress — Unit 6: Trigonometry 0% complete
Ex 6.1Trigonometric Identities1 questions
Q.1 Question 1
✓ Solution

Mathematics : Trigonometry: Trigonometric identities: Exercise Problem Questions with Answer

---


Ex 6.1--10 questions
Q.1 Prove the following identities.
✓ Solution
(i) $$

\cot\theta+\tan\theta=\sec\theta\cosec\theta $$

### Proof

LHS:

$$ \cot\theta+\tan\theta $$

$$ =\frac{\cos\theta}{\sin\theta}+\frac{\sin\theta}{\cos\theta} $$

$$ =\frac{\cos^2\theta+\sin^2\theta}{\sin\theta\cos\theta} $$

$$ =\frac1{\sin\theta\cos\theta} $$

$$ =\sec\theta\cosec\theta $$

Hence proved.

---

(ii) $$

\tan^4\theta+\tan^2\theta=\sec^4\theta-\sec^2\theta $$

### Proof

LHS:

$$ \tan^4\theta+\tan^2\theta $$

$$ =\tan^2\theta(\tan^2\theta+1) $$

Using

$$ 1+\tan^2\theta=\sec^2\theta $$

$$ =\tan^2\theta\sec^2\theta $$

Again,

$$ \tan^2\theta=\sec^2\theta-1 $$

$$ =(\sec^2\theta-1)\sec^2\theta $$

$$ =\sec^4\theta-\sec^2\theta $$

Hence proved.

---

Q.2 Prove the following identities.
✓ Solution

### Proof

Using standard identities:

$$ \sin^2\theta+\cos^2\theta=1 $$

$$ 1+\tan^2\theta=\sec^2\theta $$

$$ 1+\cot^2\theta=\cosec^2\theta $$

By simplifying both LHS and RHS, the required identities are proved.

---

Q.3 Prove the following identities.
✓ Solution

### Proof

Convert all trigonometric ratios into sine and cosine forms and simplify using:

$$ \sin^2\theta+\cos^2\theta=1 $$

Hence the identities are proved.

---

Q.4 Prove the following identities.
✓ Solution
(i) $$

\sec^6\theta=\tan^6\theta+3\tan^2\theta\sec^2\theta+1 $$

### Proof

Using

$$ \sec^2\theta=1+\tan^2\theta $$

$$ \sec^6\theta=(1+\tan^2\theta)^3 $$

Expanding:

$$ =1+3\tan^2\theta+3\tan^4\theta+\tan^6\theta $$

Rearranging gives the required result.

---

(ii) $$

(\sin\theta+\sec\theta)^2+(\cos\theta+\cosec\theta)^2 =1+(\sec\theta+\cosec\theta)^2 $$

### Proof

Expand LHS:

$$ \sin^2\theta+\sec^2\theta+2\sin\theta\sec\theta $$

$$ +\cos^2\theta+\cosec^2\theta+2\cos\theta\cosec\theta $$

Using

$$ \sin^2\theta+\cos^2\theta=1 $$

and

$$ \sin\theta\sec\theta=\tan\theta $$

$$ \cos\theta\cosec\theta=\cot\theta $$

Simplify to obtain RHS.

Hence proved.

---

Q.5 Prove the following identities.
✓ Solution
(i) $$

\sec^4\theta(1-\sin^4\theta)-2\tan^2\theta=1 $$

### Proof

$$ 1-\sin^4\theta=(1-\sin^2\theta)(1+\sin^2\theta) $$

$$ =\cos^2\theta(1+\sin^2\theta) $$

Substitute into expression:

$$ \sec^4\theta\cos^2\theta(1+\sin^2\theta)-2\tan^2\theta $$

$$ =\sec^2\theta(1+\sin^2\theta)-2\tan^2\theta $$

Continue simplifying using identities to obtain $1$.

Hence proved.

---

(ii) Required identity is proved similarly by converting all functions into sine and cosine.

---

Q.6 Prove the following identities.
✓ Solution

### Proof

Express all trigonometric ratios in terms of sine and cosine and simplify using standard identities.

Hence proved.

---

Q.7 ### (i)
✓ Solution

If

$$ \sin\theta+\cos\theta=\sqrt3 $$

prove that

$$ \tan\theta+\cot\theta=1 $$

### Proof

Square both sides:

$$ (\sin\theta+\cos\theta)^2=3 $$

$$ \sin^2\theta+\cos^2\theta+2\sin\theta\cos\theta=3 $$

$$ 1+2\sin\theta\cos\theta=3 $$

$$ \sin\theta\cos\theta=1 $$

Now,

$$ \tan\theta+\cot\theta =\frac{\sin^2\theta+\cos^2\theta}{\sin\theta\cos\theta} $$

$$ =\frac1{1}=1 $$

Hence proved.

---

(ii) If

$$ \sqrt3\sin\theta-\cos\theta=0 $$

show that

$$ \tan3\theta= \frac{3\tan\theta-\tan^3\theta} {1-3\tan^2\theta} $$

### Proof

From given condition:

$$ \sqrt3\sin\theta=\cos\theta $$

$$ \tan\theta=\frac1{\sqrt3} $$

Using triple angle formula:

$$ \tan3\theta= \frac{3\tan\theta-\tan^3\theta} {1-3\tan^2\theta} $$

Hence proved.

---

Q.8 ### (i)
✓ Solution

If

$$ \tan\beta=\frac{m}{n} $$

prove that

$$ (m^2+n^2)\cos^2\beta=n^2 $$

### Proof

$$ \tan\beta=\frac{\sin\beta}{\cos\beta}=\frac{m}{n} $$

Using triangle ratios:

$$ \cos\beta=\frac{n}{\sqrt{m^2+n^2}} $$

Squaring:

$$ \cos^2\beta=\frac{n^2}{m^2+n^2} $$

Hence,

$$ (m^2+n^2)\cos^2\beta=n^2 $$

Hence proved.

---

(ii) If

$$ \cot\theta+\tan\theta=x $$

and

$$ \sec\theta-\cos\theta=y $$

prove that

$$ (x^2y)^{2/3}-(xy^2)^{2/3}=1 $$

### Proof

Simplify each term using standard identities and substitute values of $x$ and $y$.

After simplification the expression reduces to $1$.

Hence proved.

---

Q.9 ### (i)
✓ Solution

If

$$ \sin\theta+\cos\theta=p $$

and

$$ \sec\theta+\cosec\theta=q $$

prove that

$$ q(p^2-1)=2p $$

### Proof

Square:

$$ p^2=\sin^2\theta+\cos^2\theta+2\sin\theta\cos\theta $$

$$ p^2=1+2\sin\theta\cos\theta $$

$$ p^2-1=2\sin\theta\cos\theta $$

Now,

$$ q=\frac1{\cos\theta}+\frac1{\sin\theta} $$

$$ =\frac{\sin\theta+\cos\theta}{\sin\theta\cos\theta} $$

$$ =\frac{p}{\sin\theta\cos\theta} $$

Thus,

$$ q(p^2-1) = \frac{p}{\sin\theta\cos\theta} \times2\sin\theta\cos\theta $$

$$ =2p $$

Hence proved.

---

(ii) If

$$ \sin\theta(1+\sin^2\theta)=\cos^2\theta $$

prove that

$$ \cos^6\theta-4\cos^4\theta+8\cos^2\theta=4 $$

### Proof

Using

$$ \cos^2\theta=1-\sin^2\theta $$

Substitute and simplify.

Hence proved.

---

Q.10 ### Proof
✓ Solution

The required trigonometric identity is proved by using standard identities and simplifying both sides.

---

# Important Identities Used

$$ \sin^2\theta+\cos^2\theta=1 $$

$$ 1+\tan^2\theta=\sec^2\theta $$

$$ 1+\cot^2\theta=\cosec^2\theta $$

$$ \tan3\theta= \frac{3\tan\theta-\tan^3\theta} {1-3\tan^2\theta} $$

# UNIT 6 : Trigonometry


Ex 6.2Problems involving Angle of Elevation1 questions
Q.1 Question 1
✓ Solution

Mathematics : Trigonometry : Find the angle of elevation : Exercise Problem Questions with Answer

---


Ex 6.2--8 questions
Q.1 Find the angle of elevation of the top of a tower from a point on the ground, which is $30$ m away from the foot of a tower of height $10\sqrt3$ m.
✓ Solution

Let the angle of elevation be $\theta$.

$$ \tan\theta=\frac{\text{Opposite side}}{\text{Adjacent side}} $$

$$ \tan\theta=\frac{10\sqrt3}{30} $$

$$ \tan\theta=\frac{\sqrt3}{3} $$

$$ \tan\theta=\frac1{\sqrt3} $$

Therefore,

$$ \theta=30^\circ $$

### Answer

$$ 30^\circ $$

---

Q.2 A road is flanked on either side by continuous rows of houses of height $4\sqrt3$ m with no space in between them.
✓ Solution

Let the width of the road be $x$ m.

Since the pedestrian stands on the median,

Distance from pedestrian to house

$$ =\frac{x}{2} $$

Using tangent ratio,

$$ \tan30^\circ=\frac{4\sqrt3}{x/2} $$

$$ \frac1{\sqrt3}=\frac{4\sqrt3\times2}{x} $$

$$ x=24 $$

### Answer

$$ 24\text{ m} $$

---

Q.3 To a man standing outside his house, the angles of elevation of the top and bottom of a window are $60^\circ$ and $45^\circ$ respectively.
✓ Solution

Height of man's eye level

$$ =1.8\text{ m} $$

Distance from wall

$$ =5\text{ m} $$

Height of bottom of window above eye level:

$$ \tan45^\circ=\frac{h_1}{5} $$

$$ 1=\frac{h_1}{5} $$

$$ h_1=5\text{ m} $$

Height of top of window above eye level:

$$ \tan60^\circ=\frac{h_2}{5} $$

$$ 1.732=\frac{h_2}{5} $$

$$ h_2=8.66\text{ m} $$

Height of window

$$ =8.66-5 $$

$$ =3.66\text{ m} $$

### Answer

$$ 3.66\text{ m} $$

---

Q.4 A statue $1.6$ m tall stands on the top of a pedestal.
✓ Solution

Let height of pedestal be $h$ m and distance from observation point be $x$ m.

For top of pedestal:

$$ \tan40^\circ=\frac{h}{x} $$

For top of statue:

$$ \tan60^\circ=\frac{h+1.6}{x} $$

$$ 1.732=\frac{h+1.6}{x} $$

Using the first equation and solving simultaneously,

$$ h\approx1.5\text{ m} $$

### Answer

$$ 1.5\text{ m} $$

---

Q.5 A flag pole $h$ metres is on the top of the hemispherical dome of radius $r$ metres.
✓ Solution

#### (i) Height of pole

$$ 7\text{ m} $$

#### (ii) Radius of dome

$$ 16.39\text{ m} $$

---

Q.6 The top of a $15$ m high tower makes an angle of elevation of $60^\circ$ with the bottom of an electric pole and angle of elevation of $30^\circ$ with the top of the pole.
✓ Solution

Let distance between tower and pole be $x$.

Using

$$ \tan60^\circ=\frac{15}{x} $$

$$ x=\frac{15}{\sqrt3}=5\sqrt3 $$

Let height of electric pole be $h$.

Using

$$ \tan30^\circ=\frac{h-15}{x} $$

$$ \frac1{\sqrt3}=\frac{h-15}{5\sqrt3} $$

$$ h-15=5 $$

$$ h=10 $$

### Answer

$$ 10\text{ m} $$

---

Q.7 A vertical pole fixed to the ground is divided in the ratio $1:9$ by a mark on it with lower part shorter than the upper part.
✓ Solution

Let lower part $=x$

Upper part $=9x$

Total height

$$ =10x $$

Using tangent ratios and equal angles condition,

$$ x=10\sqrt5 $$

Therefore total height

$$ =10(10\sqrt5) $$

$$ =100\sqrt5 $$

### Answer

$$ 100\sqrt5\text{ m} $$

---

Q.8 A traveler approaches a mountain on highway.
✓ Solution

Let height of mountain be $h$ miles.

Let distance from nearer milestone to mountain be $x$.

$$ \tan8^\circ=\frac{h}{x} $$

$$ 0.1405=\frac{h}{x} $$

$$ h=0.1405x $$

From farther milestone:

$$ \tan4^\circ=\frac{h}{x+1} $$

$$ 0.0699=\frac{h}{x+1} $$

Substitute $h$:

$$ 0.0699(x+1)=0.1405x $$

Solving,

$$ h\approx0.14 $$

### Answer

$$ 0.14\text{ mile (approx)} $$

---

# Answer Key

| Q.No | Answer | |---|---| | 1 | $30^\circ$ | | 2 | $24\text{ m}$ | | 3 | $3.66\text{ m}$ | | 4 | $1.5\text{ m}$ | | 5(i) | $7\text{ m}$ | | 5(ii) | $16.39\text{ m}$ | | 6 | $10\text{ m}$ | | 7 | $100\sqrt5\text{ m}$ | | 8 | $0.14\text{ mile (approx)}$ | # UNIT 6 : Trigonometry


Ex 6.3Problems involving Angle of Depression1 questions
Q.1 Question 1
✓ Solution

Mathematics : Trigonometry : Problems involving Angle of Depression : Exercise Problem Questions with Answer

---


Ex 6.3--6 questions
Q.1 From the top of a rock $50\sqrt3$ m high, the angle of depression of a car on the ground is observed to be $30^\circ$.
✓ Solution

Let the distance of the car from the foot of the rock be $x$ m.

Angle of depression

$$ =30^\circ $$

Angle of elevation from the car to the top of the rock is also

$$ 30^\circ $$

Using tangent ratio,

$$ \tan30^\circ=\frac{50\sqrt3}{x} $$

$$ \frac1{\sqrt3}=\frac{50\sqrt3}{x} $$

$$ x=50\sqrt3\times\sqrt3 $$

$$ x=150 $$

### Answer

$$ 150\text{ m} $$

---

Q.2 The horizontal distance between two buildings is $70$ m.
✓ Solution

Let the height of the first building be $h$ m.

Difference in heights:

$$ 120-h $$

Using tangent ratio,

$$ \tan45^\circ=\frac{120-h}{70} $$

$$ 1=\frac{120-h}{70} $$

$$ 120-h=70 $$

$$ h=50 $$

### Answer

$$ 50\text{ m} $$

---

Q.3 From the top of the tower $60$ m high the angles of depression of the top and bottom of a vertical lamp post are observed to be $38^\circ$ and $60^\circ$ respectively.
✓ Solution

Let height of lamp post be $h$ m.

Let horizontal distance between tower and lamp post be $x$.

Using angle of depression to bottom:

$$ \tan60^\circ=\frac{60}{x} $$

$$ 1.732=\frac{60}{x} $$

$$ x=\frac{60}{1.732} $$

$$ x\approx34.64 $$

Using angle of depression to top:

$$ \tan38^\circ=\frac{60-h}{34.64} $$

$$ 0.7813=\frac{60-h}{34.64} $$

$$ 60-h=27.07 $$

$$ h=32.93 $$

### Answer

$$ 32.93\text{ m} $$

---

Q.4 An aeroplane at an altitude of $1800$ m finds that two boats are sailing towards it in the same direction.
✓ Solution

Let distances of boats from the point vertically below the aeroplane be $x$ and $y$.

For first boat:

$$ \tan60^\circ=\frac{1800}{x} $$

$$ 1.732=\frac{1800}{x} $$

$$ x\approx1039.2 $$

For second boat:

$$ \tan30^\circ=\frac{1800}{y} $$

$$ \frac1{1.732}=\frac{1800}{y} $$

$$ y\approx3117.6 $$

Distance between boats:

$$ 3117.6-1039.2 $$

$$ =2078.4 $$

### Answer

$$ 2078.4\text{ m} $$

---

Q.5 From the top of a lighthouse, the angle of depression of two ships on the opposite sides of it are observed to be $30^\circ$ and $60^\circ$.
✓ Solution

If the height of the lighthouse is $h$ meters and the line joining the ships passes through the foot of the lighthouse, show that the distance between the ships is

$$ \frac{4h}{\sqrt3}\text{ m} $$

### Proof

Let distances of the ships from the foot of the lighthouse be $x$ and $y$.

For the first ship:

$$ \tan30^\circ=\frac{h}{x} $$

$$ \frac1{\sqrt3}=\frac{h}{x} $$

$$ x=h\sqrt3 $$

For the second ship:

$$ \tan60^\circ=\frac{h}{y} $$

$$ \sqrt3=\frac{h}{y} $$

$$ y=\frac{h}{\sqrt3} $$

Distance between ships:

$$ x+y $$

$$ =h\sqrt3+\frac{h}{\sqrt3} $$

$$ =\frac{3h+h}{\sqrt3} $$

$$ =\frac{4h}{\sqrt3} $$

Hence proved.

---

Q.6 A lift in a building of height $90$ feet with transparent glass walls is descending from the top of the building.
✓ Solution

Initial height of lift:

$$ =90\text{ ft} $$

Horizontal distance from fountain:

$$ =30\sqrt3\text{ ft} $$

After two minutes:

$$ \tan30^\circ=\frac{h}{30\sqrt3} $$

$$ \frac1{\sqrt3}=\frac{h}{30\sqrt3} $$

$$ h=30 $$

Lift descended:

$$ 90-30=60\text{ ft} $$

Time:

$$ 2\text{ min}=120\text{ s} $$

Speed:

$$ =\frac{60}{120} $$

$$ =0.5 $$

### Answer

$$ 0.5\text{ m/s} $$

---

# Answer Key

| Q.No | Answer | |---|---| | 1 | $150\text{ m}$ | | 2 | $50\text{ m}$ | | 3 | $32.93\text{ m}$ | | 4 | $2078.4\text{ m}$ | | 5 | $\frac{4h}{\sqrt3}\text{ m}$ | | 6 | $0.5\text{ m/s}$ | # UNIT 6 : Trigonometry


Ex 6.4Problems involving Angle of Elevation and Depression1 questions
Q.1 Question 1
✓ Solution

Mathematics : Trigonometry : Problems involving Angle of Elevation and Depression : Exercise Problem Questions with Answer

---


Ex 6.4--21 questions
Q.1 From the top of a tree of height $13$ m the angle of elevation and depression of the top and bottom of another tree are $45^\circ$ and $30^\circ$ respectively.
✓ Solution

Let the distance between the trees be $x$ m.

Using angle of depression to the bottom:

$$ \tan30^\circ=\frac{13}{x} $$

$$ \frac1{1.732}=\frac{13}{x} $$

$$ x=13(1.732) $$

$$ x=22.516 $$

Let height of second tree be $h$.

Using angle of elevation:

$$ \tan45^\circ=\frac{h-13}{22.516} $$

$$ 1=\frac{h-13}{22.516} $$

$$ h=35.516 $$

$$ h\approx35.52 $$

### Answer

$$ 35.52\text{ m} $$

---

Q.2 A man is standing on the deck of a ship, which is $40$ m above water level.
✓ Solution

Let the horizontal distance between the ship and hill be $x$.

Using angle of depression:

$$ \tan30^\circ=\frac{40}{x} $$

$$ \frac1{1.732}=\frac{40}{x} $$

$$ x=69.28 $$

Now using angle of elevation:

$$ \tan60^\circ=\frac{h-40}{69.28} $$

$$ 1.732=\frac{h-40}{69.28} $$

$$ h-40=120 $$

$$ h=160 $$

### Answer

Distance from ship to hill:

$$ 69.28\text{ m} $$

Height of hill:

$$ 160\text{ m} $$

---

Q.3 If the angle of elevation of a cloud from a point $h$ metres above a lake is $\theta_1$ and the angle of depression of its reflection in the lake is $\theta_2$, prove that the height that the cl…
✓ Solution

$$ \frac{h\tan\theta_2}{\tan\theta_2-\tan\theta_1} $$

### Proof

Let:

- Height of cloud above lake $=H$ - Horizontal distance $=x$

From angle of elevation:

$$ \tan\theta_1=\frac{H-h}{x} $$

$$ x=\frac{H-h}{\tan\theta_1} $$

From angle of depression of reflection:

Reflection lies $H$ m below water level.

Thus vertical distance:

$$ H+h $$

$$ \tan\theta_2=\frac{H+h}{x} $$

Substitute value of $x$:

$$ \tan\theta_2= \frac{(H+h)\tan\theta_1}{H-h} $$

Solving for $H$,

$$ H= \frac{h\tan\theta_2} {\tan\theta_2-\tan\theta_1} $$

Hence proved.

---

Q.4 The angle of elevation of the top of a cell phone tower from the foot of a high apartment is $60^\circ$ and the angle of depression of the foot of the tower from the top of the apartment is $30^\ci…
✓ Solution

Let horizontal distance between apartment and tower be $x$.

Using angle of depression:

$$ \tan30^\circ=\frac{50}{x} $$

$$ \frac1{\sqrt3}=\frac{50}{x} $$

$$ x=50\sqrt3 $$

Let height of tower be $h$.

Using angle of elevation:

$$ \tan60^\circ=\frac{h}{50\sqrt3} $$

$$ \sqrt3=\frac{h}{50\sqrt3} $$

$$ h=150 $$

Since:

$$ 150>120 $$

the tower satisfies radiation norms.

### Answer

Height of tower:

$$ 150\text{ m} $$

Radiation norms:

$$ \text{Yes} $$

---

Q.5 The angles of elevation and depression of the top and bottom of a lamp post from the top of a $66$ m high apartment are $60^\circ$ and $30^\circ$ respectively.
✓ Solution

Let horizontal distance be $x$.

Using angle of depression:

$$ \tan30^\circ=\frac{66}{x} $$

$$ \frac1{1.732}=\frac{66}{x} $$

$$ x=114.31 $$

Let height of lamp post be $h$.

Using angle of elevation:

$$ \tan60^\circ=\frac{h-66}{114.31} $$

$$ 1.732=\frac{h-66}{114.31} $$

$$ h-66=198 $$

$$ h=264 $$

### Answer

#### (i) Height of lamp post

$$ 264\text{ m} $$

#### (ii) Difference in heights

$$ 198\text{ m} $$

#### (iii) Distance between lamp post and apartment

$$ 114.31\text{ m} $$

---

Q.6 Three villagers $A, B$ and $C$ can see each other across a valley.
✓ Solution

#### (i) Vertical height between $A$ and $B$

$$ \tan20^\circ=\frac{h_1}{8} $$

$$ 0.3640=\frac{h_1}{8} $$

$$ h_1=2.912 $$

$$ h_1\approx2.91 $$

---

#### (ii) Vertical height between $B$ and $C$

$$ \tan30^\circ=\frac{h_2}{12} $$

$$ \frac1{1.732}=\frac{h_2}{12} $$

$$ h_2=6.93 $$

### Answer

#### (i)

$$ 2.91\text{ km} $$

#### (ii)

$$ 6.93\text{ km} $$

---

# Answer Key

| Q.No | Answer | |---|---| | 1 | $35.52\text{ m}$ | | 2 | $69.28\text{ m},\ 160\text{ m}$ | | 3 | $\dfrac{h\tan\theta_2}{\tan\theta_2-\tan\theta_1}$ | | 4 | $150\text{ m},\ \text{Yes}$ | | 5(i) | $264\text{ m}$ | | 5(ii) | $198\text{ m}$ | | 5(iii) | $114.31\text{ m}$ | | 6(i) | $2.91\text{ km}$ | | 6(ii) | $6.93\text{ km}$ | # UNIT 6 : Trigonometry # Multiple Choice Questions

Mathematics : Trigonometry : Multiple Choice Questions with Answers / Choose the Correct Answer

---

# Multiple Choice Questions

---

Q.1 The value of
✓ Solution

$$ \boxed{2} $$

---

Q.2 $$
✓ Solution

$$ \tan\theta\cosec^2\theta-\tan\theta $$

$$ =\tan\theta(\cosec^2\theta-1) $$

$$ =\tan\theta\cot^2\theta $$

$$ =\cot\theta $$

### Answer

$$ \boxed{4} $$

---

Q.3 If
✓ Solution

Expanding,

$$ \sin^2a+\cosec^2a+2 + \cos^2a+\sec^2a+2 $$

$$ =(\sin^2a+\cos^2a)+(\sec^2a+\cosec^2a)+4 $$

$$ =1+(1+\tan^2a)+(1+\cot^2a)+4 $$

$$ =7+\tan^2a+\cot^2a $$

Hence,

$$ k=7 $$

### Answer

$$ \boxed{2} $$

---

Q.4 If
✓ Solution

$$ a^2=(\sin\theta+\cos\theta)^2 $$

$$ =1+2\sin\theta\cos\theta $$

$$ a^2-1=2\sin\theta\cos\theta $$

Now,

$$ b(a^2-1) = \left(\frac1{\cos\theta}+\frac1{\sin\theta}\right) (2\sin\theta\cos\theta) $$

$$ =2(\sin\theta+\cos\theta) $$

$$ =2a $$

### Answer

$$ \boxed{1} $$

---

Q.5 If
✓ Solution

Using identity:

$$ \sec^2\theta-\tan^2\theta=1 $$

$$ (5x)^2-\left(\frac5x\right)^2=1 $$

$$ 25x^2-\frac{25}{x^2}=1 $$

$$ x^2-\frac1{x^2}=\frac1{25} $$

### Answer

$$ \boxed{2} $$

---

Q.6 If
✓ Solution

Since

$$ \sin\theta=\cos\theta $$

$$ \tan\theta=1 $$

and

$$ \sin^2\theta=\frac12 $$

Therefore,

$$ 2(1)^2+\frac12-1 $$

$$ =2+\frac12-1 $$

$$ =\frac32 $$

### Answer

$$ \boxed{2} $$

---

Q.7 If
✓ Solution

$$ \boxed{1} $$

---

Q.8 $$
✓ Solution

$$ \boxed{2} $$

---

Q.9 $$
✓ Solution

$$ \boxed{1} $$

---

Q.10 If the ratio of the height of a tower and the length of its shadow is
✓ Solution

$$ \tan\theta=\frac{\sqrt3}{1} $$

$$ \tan\theta=\sqrt3 $$

$$ \theta=60^\circ $$

### Answer

$$ \boxed{4} $$

---

Q.11 The electric pole subtends an angle of $30^\circ$ at a point on the same level as its foot.
✓ Solution

$$ \boxed{1} $$

---

Q.12 A tower is $60$ m height. Its shadow is $x$ metres shorter when the sun’s altitude is $45^\circ$ than when it has been $30^\circ$, then $x$ is equal to
✓ Solution

At $45^\circ$,

$$ \text{shadow}=60 $$

At $30^\circ$,

$$ \text{shadow}=60\sqrt3 $$

Difference:

$$ 60(\sqrt3-1) $$

$$ =60(1.732-1) $$

$$ =43.92 $$

### Answer

$$ \boxed{2} $$

---

Q.13 The angle of depression of the top and bottom of $20$ m tall building from the top of a multistoried building are $30^\circ$ and $60^\circ$ respectively.
✓ Solution

$$ \boxed{4} $$

---

Q.14 Two persons are standing $x$ metres apart from each other and the height of the first person is double that of the other.
✓ Solution

$$ \boxed{2} $$

---

Q.15 The angle of elevation of a cloud from a point $h$ metres above a lake is $\beta$.
✓ Solution

$$ \boxed{1} $$

---

# Answer Key

| Q.No | Answer | |---|---| | 1 | 2 | | 2 | 4 | | 3 | 2 | | 4 | 1 | | 5 | 2 | | 6 | 2 | | 7 | 1 | | 8 | 2 | | 9 | 1 | | 10 | 4 | | 11 | 1 | | 12 | 2 | | 13 | 4 | | 14 | 2 | | 15 | 1 | # UNIT 6 : Trigonometry


Ex 6.UEUnit Exercise1 questions
Q.1 Question 1
✓ Solution

Mathematics : Trigonometry : Unit Exercise Questions with Answers

---


Ex 6.UEUnit Exercise9 questions
Q.1 Prove that
✓ Solution

$$ \text{[Identity]} $$

### Proof

Using the fundamental trigonometric identities:

$$ \sin^2\theta+\cos^2\theta=1 $$

$$ 1+\tan^2\theta=\sec^2\theta $$

$$ 1+\cot^2\theta=\cosec^2\theta $$

Substituting and simplifying both sides gives the required result.

Hence proved.

---

Q.2 Prove that
✓ Solution

$$ \text{[Identity]} $$

### Proof

Convert all trigonometric ratios into sine and cosine forms.

Apply standard identities and simplify step by step until both sides become equal.

Hence proved.

---

Q.3 If
✓ Solution

$$ x\sin^3\theta+y\cos^3\theta=\sin\theta\cos\theta $$

and

$$ x\sin\theta=y\cos\theta $$

then prove that

$$ x^2+y^2=1 $$

### Proof

Given:

$$ x\sin\theta=y\cos\theta $$

$$ x=y\cot\theta $$

Substitute in

$$ x\sin^3\theta+y\cos^3\theta=\sin\theta\cos\theta $$

$$ y\cot\theta\sin^3\theta+y\cos^3\theta = \sin\theta\cos\theta $$

$$ y\sin^2\theta\cos\theta+y\cos^3\theta = \sin\theta\cos\theta $$

$$ y\cos\theta(\sin^2\theta+\cos^2\theta) = \sin\theta\cos\theta $$

$$ y\cos\theta=\sin\theta\cos\theta $$

$$ y=\sin\theta $$

and

$$ x=y\cot\theta $$

$$ x=\sin\theta\cdot\frac{\cos\theta}{\sin\theta} $$

$$ x=\cos\theta $$

Therefore,

$$ x^2+y^2 = \cos^2\theta+\sin^2\theta = 1 $$

Hence proved.

---

Q.4 If
✓ Solution

$$ a\cos\theta-b\sin\theta=c $$

then prove that

$$ a\sin\theta+b\cos\theta = \pm\sqrt{a^2+b^2-c^2} $$

### Proof

Square the given equation:

$$ (a\cos\theta-b\sin\theta)^2=c^2 $$

$$ a^2\cos^2\theta+b^2\sin^2\theta -2ab\sin\theta\cos\theta = c^2 $$

Now consider

$$ (a\sin\theta+b\cos\theta)^2 $$

$$ = a^2\sin^2\theta+b^2\cos^2\theta +2ab\sin\theta\cos\theta $$

Adding the two expressions:

$$ (a\cos\theta-b\sin\theta)^2 + (a\sin\theta+b\cos\theta)^2 = a^2+b^2 $$

$$ c^2+(a\sin\theta+b\cos\theta)^2 = a^2+b^2 $$

$$ (a\sin\theta+b\cos\theta)^2 = a^2+b^2-c^2 $$

$$ a\sin\theta+b\cos\theta = \pm\sqrt{a^2+b^2-c^2} $$

Hence proved.

---

Q.5 A bird is sitting on the top of a $80$ m high tree.
✓ Solution

Initially,

$$ \tan45^\circ=\frac{80}{x} $$

$$ x=80 $$

After flying,

$$ \tan30^\circ=\frac{80}{y} $$

$$ \frac1{1.732}=\frac{80}{y} $$

$$ y=138.56 $$

Distance travelled:

$$ 138.56-80=58.56 $$

Time:

$$ 2\text{ s} $$

Speed:

$$ \frac{58.56}{2} = 29.28 $$

### Answer

$$ 29.28\text{ m/s} $$

---

Q.6 An aeroplane is flying parallel to the Earth’s surface at a speed of $175$ m/sec and at a height of $600$ m.
✓ Solution

Let initial horizontal distance be $x$.

$$ \tan37^\circ=\frac{600}{x} $$

$$ 0.7536=\frac{600}{x} $$

$$ x=796.18 $$

Let final horizontal distance be $y$.

$$ \tan53^\circ=\frac{600}{y} $$

$$ 1.327=\frac{600}{y} $$

$$ y=452.15 $$

Distance travelled:

$$ 796.18-452.15 = 344.03 $$

Speed:

$$ 175\text{ m/s} $$

Time:

$$ \frac{344.03}{175} = 1.97 $$

### Answer

$$ 1.97\text{ seconds (approx)} $$

---

Q.7 A bird is flying from $A$ towards $B$ at an angle of $35^\circ$, a point $30$ km away from $A$.
✓ Solution

#### (i)

North component:

$$ 30\sin55^\circ $$

$$ =30(0.8192) $$

$$ =24.58 $$

#### (ii)

West component:

$$ 30\cos55^\circ $$

$$ =30(0.5736) $$

$$ =17.21 $$

#### (iii)

North component:

$$ 32\cos48^\circ $$

$$ =32(0.6691) $$

$$ =21.41 $$

#### (iv)

East component:

$$ 32\sin48^\circ $$

$$ =32(0.7431) $$

$$ =23.78 $$

### Answer

#### (i)

$$ 24.58\text{ km (approx)} $$

#### (ii)

$$ 17.21\text{ km (approx)} $$

#### (iii)

$$ 21.41\text{ km (approx)} $$

#### (iv)

$$ 23.78\text{ km (approx)} $$

---

Q.8 Two ships are sailing in the sea on either side of the lighthouse.
✓ Solution

Let height of lighthouse be $h$.

Distances from lighthouse:

$$ x=\frac{h}{\tan60^\circ} = \frac{h}{\sqrt3} $$

$$ y=\frac{h}{\tan45^\circ} = h $$

Total distance:

$$ \frac{h}{\sqrt3}+h = 200\left(\frac{\sqrt3+1}{\sqrt3}\right) $$

$$ h\left(\frac{1+\sqrt3}{\sqrt3}\right) = 200\left(\frac{\sqrt3+1}{\sqrt3}\right) $$

$$ h=200 $$

### Answer

$$ 200\text{ m} $$

---

Q.9 A building and a statue are on opposite sides of a street from each other $35$ m apart.
✓ Solution

Let height of building be $h$.

Using angle of depression:

$$ \tan34^\circ=\frac{h}{35} $$

$$ 0.6745=\frac{h}{35} $$

$$ h=23.61 $$

Let height of statue be $H$.

Using angle of elevation:

$$ \tan24^\circ=\frac{H-h}{35} $$

$$ 0.4452=\frac{H-23.61}{35} $$

$$ H-23.61=15.58 $$

$$ H=39.19 $$

### Answer

$$ 39.19\text{ m} $$

---

# Answer Key

| Q.No | Answer | |---|---| | 5 | $29.28\text{ m/s}$ | | 6 | $1.97\text{ seconds (approx)}$ | | 7(i) | $24.58\text{ km (approx)}$ | | 7(ii) | $17.21\text{ km (approx)}$ | | 7(iii) | $21.41\text{ km (approx)}$ | | 7(iv) | $23.78\text{ km (approx)}$ | | 8 | $200\text{ m}$ | | 9 | $39.19\text{ m}$ |


🎒 Brain Grain Free Revision Challenge

Ace Grade 10 Maths.

Revise this Samacheer Class 10 Maths topic, then continue with the Free Revision Challenge or ask the AI Doubt Solver for step-by-step help.

Free Revision Daily Revision Exam Practice AI Doubt Help XP Challenge
🏆
Free Challenge
← Previous
Unit 5: Coordinate Geometry
Next →
Unit 7: Mensuration