WORD PROBLEMS INVOLVING ANGLE OF ELEVATION AND …

Republic of the Philippines

Department of Education Regional Office IX, Zamboanga Peninsula

Zest for Progress

Zeal of Partnership

9

4th QUARTER – Module 4: WORD PROBLEMS INVOLVING

ANGLE OF ELEVATION AND DEPRESSION

Name of Learner: ___________________________

Grade & Section: ___________________________

Name of School: ___________________________

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Mathematics – Grade 9 Alternative Delivery Mode Quarter 4 - Module 4: Word Problems Involving Angle of Elevation and Depression First Edition, 2020

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Published by the Department of Education Secretary: Leonor Magtolis Briones Undersecretary: Diosdado M. San Antonio

Printed in the Philippines

Department of Education – Region IX, Zamboanga Peninsula

Office Address: Tiguma, Airport Road, Pagadian City

Telefax: (062) – 215 – 3751; 991 – 5975

E-mail Address: [email protected]

Development Team of the Module

Writer: Sandra D. Ortega

Editors: Mary Rose A. Castillo

Shirly V. Gajilomo

Illustrator: Sandra D. Ortega

Reviewers: EPS, Mathematics Vilma A. Brown, Ed. D.

Principal Mujim U. Abdurahim

Management Team: SDS Roy C. Tuballa, EMD, JD, CESO VI

ASDS Jay S. Montealto, CESO VI

ASDS Norma T. Francisco, DM, CESE

EPS Mathematics Vilma A. Brown, Ed. D.

EPS LRMS Aida F. Coyme, Ed. D.

2

Introductory Message

This Self – Learning Module (SLM) is prepared so that you, our dear learners, can continue

your studies and learn while at home. Activities, questions, directions, exercises, and

discussions are carefully stated for you to understand each lesson.

Each SLM is composed of different parts. Each part shall guide you step-by-step as you

discover and understand the lesson prepared for you.

Pre-tests are provided to measure your prior knowledge on lessons in each SLM. This will tell

you if you can proceed on completing this module or if you need to ask your facilitator or your

teacher’s assistance for better understanding of the lesson. At the end of each module, you

need to answer the post-test to self-check your learning. Answer keys are provided for each

activity and test. We trust that you will be honest in using these.

In addition to the material in the main text, Notes to the Teacher are also provided to our

facilitators and parents for strategies and reminders on how they can best help you on your

home-based learning.

Please use this module with care. Do not put unnecessary marks on any part of this SLM. Use

a separate sheet of paper in answering the exercises and tests. Read the instructions carefully

before performing each task.

If you have any questions in using this SLM or any difficulty in answering the tasks in this

module, do not hesitate to consult your teacher or facilitator.

Thank you.

In this module, it is a prerequisite to have the skill in illustrating angle of elevation and

angle of depression. When solving a word problem involving angle of elevation and angle of

depression, it is a good practice to draw the right triangle, illustrate and label the parts properly

to easily identify the unknowns. Then use appropriate trigonometric ratios to find the missing

parts. The skills to be developed in this lesson imposes the realization of the twin goals of

Mathematics – problem solving and critical thinking.

After going through this module, you should be able to:

⚫ illustrate angle of elevation and angle of depression. (M9GE– IVd – 1)

⚫ solve word problems involving angle of elevation and angle of depression

What I Need to Know

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height (h) height (h)

height (h) height (h)

What I Know

Directions: Choose the letter that corresponds to your answer. Write your answer on a

separate sheet.

For items 1 to 3, refer to this problem.

“A bahay kubo is 9 meters away from a tree. If the angle of elevation is 55 from the bahay

kubo to the top of the tree, how high is the tree?”

[1] Which of the following is the correct illustration to the problem?

A. B.

C. D.

[2] What trigonometric ratio must be used to solve the problem?

A. sin 55° =ℎ

9 B. cos 55° =

ℎ

9 C. tan 55° =

ℎ

9 D. csc 55° =

9

ℎ

[3] What is the answer to the problem?

A. The height of the tree is 12.85 meters. B. The height of the tree is 10.99 meters. C. The height of the tree is 7.37 meters. D. The height of the tree is 5.16 meters.

[4] Based on the figure at the right, if the angle of elevation (a) is 43 and the distance of the man from the flagpole is 7 meters, what is the value of c?

A. 4.77 meters B. 5.11 meters C. 6.53 meters D. 9.57 meters

[5] Using the given in item number 4, if the angle of

depression (b) is 40, what is the height of the flagpole? A. 9.27 meters B. 10.48 meters C. 12.40 meters D. 18.71 meters

c

Note: The student may use scientific calculator to easily

compute the measure of the unknowns.

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LESSON

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WORD PROBLEMS INVOLVING

ANGLE OF ELEVATION AND

ANGLE OF DEPRESSION

What’s In

From the previous module, you have illustrated the angle of elevation and depression

and used trigonometric ratios to find the other parts of a right triangle. This time, let’s check

your prior knowledge.

DIRECTIONS: Draw the line of sight to the birds then identify if the angle formed is an angle of elevation or an angle of depression. Then, answer the problem on a separate sheet of paper.

Draw It! ACTIVITY

Angle formed: _________________

PROBLEM: “Based on the picture, if the distance of the man to the birds is 25 miles and the

height of the birds from man’s eye level is 5 miles, what is the measure of the angle formed

from the man’s eyes to the birds?” (Write the answer in the nearest degree.)

5 miles

25 miles

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You are standing on a 10-foot tree house, looking down at a certain point where the ball hit the ground makes an angle of depression of

37, how far is that point from the base of the tree?

In this section, you will be provided with an opportunity to discover and solve problems

in daily life through the following activities.

DIRECTIONS: Label the diagram and solve the problem on a separate sheet of paper. Then,

answer the guide questions below. Write the answer in the nearest whole number.

Guide Questions:

[1] How did you label the information presented in the

problem?

[2] What is being asked in the problem?

[3] What trigonometric ratio did you use to find the distance of

the point from the base of the tree?

“Suppose you are on top of a mountain, looking down at a certain building, how will

you directly measure the height of the mountain?” In this section, you will discover how to

solve word problems involving angle of elevation and angle of depression. The trigonometric

ratios you have learned in the previous module will help you answer such problems.

ILLUSTRATIVE EXAMPLE 1:

A building is 16 meters high. At a certain distance away from the building, an

observer determines that the angle of elevation to the top of it is 35. How far is the

observer from the base of the building? (Write the answer to the nearest whole number.)

Bouncing Ball! ACTIVITY

What are the steps in solving word problems involving

angle of elevation and depression?

What’s New

What is It

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STEPS IN SOLVING WORD PROBLEM:

Step 1: Draw and label the diagram.

Step 2: Identify what is asked in the problem.

The distance between the observer and

the base of the building.

Step 3: Use appropriate trigonometric ratio to

solve the problem. Since the two legs of the right triangle

are part of the problem, hence we use

tangent ratio: 𝒕𝒂𝒏𝟑𝟓° =𝟏𝟔

𝒅

Step 4: Solution and interpretation.

𝒕𝒂𝒏𝟑𝟓° =𝟏𝟔

𝒅

(𝒅)𝒕𝒂𝒏𝟑𝟓° =𝟏𝟔

𝒅(𝒅)

(𝒅)𝒕𝒂𝒏𝟑𝟓°

𝒕𝒂𝒏𝟑𝟓°=

𝟏𝟔

𝒕𝒂𝒏𝟑𝟓°

𝒅 =𝟏𝟔

𝒕𝒂𝒏𝟑𝟓°

𝒅 = 𝟐𝟐. 𝟖𝟓 ≈ 𝟐𝟑 𝒎𝒆𝒕𝒆𝒓𝒔

Hence, the observer is approximately 23

meters away from the base of the building.

ILLUSTRATIVE EXAMPLE 2:

An airplane is flying at a height of 5 kilometers above the ground. The distance

along the ground from the airplane to the airport is 7 kilometers. What is the angle of

depression from the airplane to the airport? (Write the answer to the nearest degree.)




The angle of depression from the

airplane to the airport.


solve the problem. Since the two legs of the right triangle

are part of the problem, hence we use

tangent ratio: 𝒕𝒂𝒏𝑨° =𝟓

𝟕


𝒕𝒂𝒏𝑨 =𝟓

𝟕

𝑨 = 𝒕𝒂𝒏−𝟏 (𝟓

𝟕)

𝑨 = 𝟑𝟓. 𝟓𝟒 ≈ 𝟑𝟔°

Hence, the angle of depression from the

airplane to the airport is approximately 36.

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PROBLEM: “A 5-meter ladder is leaning against the wall of a

house. The foot of the ladder on the ground is 1.5 meters from the

wall. What angle measure does the ladder make with the wall?”

You have just learned how to draw pictures presented by the information in the

given problems. Using this skill, you can now practice illustrating a word problem and

solving problems involving angle of elevation and depression.

What’s More

Now that you have a deeper understanding of the lesson, you are ready to do the

activity in this section. Your goal is to apply your learning to solve word problems involving

angle of elevation and depression. You will be given a real-life problem which you will illustrate,

label the identified parts, and solve for the unknown part using the trigonometric ratios.

DIRECTIONS: Answer the problem below by following the steps in the table. Write the answer

in the nearest degree.




_________________________________


solve the problem. _________________________________

_________________________________


__________________________________

__________________________________

Sketch My Problem! ACTIVITY

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STEP 1:

STEP 2:

STEP 3:

STEP 4:

STEPS IN SOLVING WORD PROBLEMS INVOLVING ANGLE OF

ELEVATION AND DEPRESSION

What I Have Learned

Find out how much you have learned from this module by filling in the steps in solving

word problems involving angle of elevation and depression in the rolled paper chain. Write

your answer on a separate sheet of paper.

What I Can Do

Here is another activity that will let you transfer your knowledge and skill into real life

situations.

Objective: To apply sine, cosine, or tangent ratios to find the angle of elevation or depression.

Materials: Tape measure, pen and paper

Directions: You should work with a partner to do the activity. Write your answers on a

separate sheet of paper.

Fill Me In! ACTIVITY

What can I Learn from my Shadow? ACTIVITY

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Procedure:

[1] Ask your partner to measure your height (in meter) using the tape measure.

[2] Go outside your house at 3:00 o’clock in the afternoon and stand under the sun.

[3] Ask your partner to measure the length of your shadow.

[4] Using what you know about trigonometric ratios, determine the angle of depression from

your eye level to the tip of your shadow. (Sketch a picture of the situation that will help in your

computation. Write the answer in the nearest degree.)

Assessment

Directions: Read and understand each item carefully. Choose the letter that corresponds to

your answer. Write your answer on a separate sheet.

For items 1 to 5, refer to the problem below.

“A kite is held by 125 meters of string makes an angle of elevation with the ground of 45o. About how high is the kite above the ground?”

[1] Which is the correct illustration to the problem?

A. B.

C. D. [2] What is the hypotenuse in the problem?

A. 125cm B. 125m C. 45o D. the unknown

[3] What is asked in the problem? A. Length of the string B. Height of the kite from the ground C. Angle of elevation D. Distance of the man from the kite

[4] What trigonometric ratio must be used to solve the problem? A. Sine B. Cosine C. Tangent D. Cosecant

[5] What is the answer to the given problem?

A. 113.6m B. 88.4m C. 75.1m D. 62.8m

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c

For items 6 to 8, refer to the problem below.

“From the top of a tower, a man finds that the angle of depression of a car on the ground is

30o. If the car is at a distance of 40 meters from the tower, find the height of the tower.”

[6] Which is the correct illustration to the problem?

A. B.

C. D.

[7] What trigonometric ratio must be used to solve the problem? A. Sine B. Cosine C. Tangent D. Cosecant

[8] What is the answer to the problem?

A. 80 meters B. 69.28 meters C. 23.09 meters D. 20 meters

[9] Based on the figure at the right, what is the angle of elevation?

A. a B. b C. c D. None

[10] If a = 45 and the distance of the man from the flagpole is 6 meters,

what is the value of c?

A. 8.48 meters B. 6 meters

C. 4.24 meters D. 2.44 meters

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Answer Key

What I Know:

1. B 2. C 3. A 4. C 5. C

What’s In:

Angle formed: elevation The measure of the angle of elevation is 11o.

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What I Can Do:

Answers may vary.

Assessment:

1. D 2. A 3. B 4. A 5. B

6. A 7. C 8. C 9. A 10. B

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References:

Bryant, Merden, Mathematics 9 Learner’s Material. Pasig City: Department of Education,

2014.

15

I AM A FILIPINO

by Carlos P. Romulo

I am a Filipino – inheritor of a glorious past, hostage to the

uncertain future. As such, I must prove equal to a two-fold

task – the task of meeting my responsibility to the past, and

the task of performing my obligation to the future.

I am sprung from a hardy race – child many generations

removed of ancient Malayan pioneers. Across the centuries,

the memory comes rushing back to me: of brown-skinned

men putting out to sea in ships that were as frail as their hearts

were stout. Over the sea I see them come, borne upon the

billowing wave and the whistling wind, carried upon the

mighty swell of hope – hope in the free abundance of the new

land that was to be their home and their children’s forever.

This is the land they sought and found. Every inch of shore

that their eyes first set upon, every hill and mountain that

beckoned to them with a green and purple invitation, every

mile of rolling plain that their view encompassed, every river

and lake that promised a plentiful living and the fruitfulness

of commerce, is a hollowed spot to me.

By the strength of their hearts and hands, by every right of

law, human and divine, this land and all the appurtenances

thereof – the black and fertile soil, the seas and lakes and

rivers teeming with fish, the forests with their inexhaustible

wealth in wild and timber, the mountains with their bowels

swollen with minerals – the whole of this rich and happy land

has been for centuries without number, the land of my

fathers. This land I received in trust from them, and in trust

will pass it to my children, and so on until the world is no

more.

I am a Filipino. In my blood runs the immortal seed of heroes

– seed that flowered down the centuries in deeds of courage

and defiance. In my veins yet pulses the same hot blood that

sent Lapulapu to battle against the alien foe, that drove Diego

Silang and Dagohoy into rebellion against the foreign

oppressor.

That seed is immortal. It is the self-same seed that flowered

in the heart of Jose Rizal that morning in Bagumbayan when

a volley of shots put an end to all that was mortal of him and

made his spirit deathless forever; the same that flowered in

the hearts of Bonifacio in Balintawak, of Gregorio del Pilar

at Tirad Pass, of Antonio Luna at Calumpit, that bloomed in

flowers of frustration in the sad heart of Emilio Aguinaldo at

Palanan, and yet burst forth royally again in the proud heart

of Manuel L. Quezon when he stood at last on the threshold

of ancient Malacanang Palace, in the symbolic act of

possession and racial vindication. The seed I bear within me

is an immortal seed.

It is the mark of my manhood, the symbol of my dignity as

a human being. Like the seeds that were once buried in the

tomb of Tutankhamen many thousands of years ago, it shall

grow and flower and bear fruit again. It is the insigne of my

race, and my generation is but a stage in the unending

search of my people for freedom and happiness.

I am a Filipino, child of the marriage of the East and the

West. The East, with its languor and mysticism, its passivity

and endurance, was my mother, and my sire was the West

that came thundering across the seas with the Cross and

Sword and the Machine. I am of the East, an eager

participant in its struggles for liberation from the imperialist

yoke. But I know also that the East must awake from its

centuried sleep, shake off the lethargy that has bound its

limbs, and start moving where destiny awaits.

For I, too, am of the West, and the vigorous peoples of the

West have destroyed forever the peace and quiet that once

were ours. I can no longer live, a being apart from those

whose world now trembles to the roar of bomb and cannon

shot. For no man and no nation is an island, but a part of the

main, and there is no longer any East and West – only

individuals and nations making those momentous choices

that are the hinges upon which history revolves. At the

vanguard of progress in this part of the world I stand – a

forlorn figure in the eyes of some, but not one defeated and

lost. For through the thick, interlacing branches of habit and

custom above me I have seen the light of the sun, and I

know that it is good. I have seen the light of justice and

equality and freedom, my heart has been lifted by the vision

of democracy, and I shall not rest until my land and my

people shall have been blessed by these, beyond the power

of any man or nation to subvert or destroy.

I am a Filipino, and this is my inheritance. What pledge

shall I give that I may prove worthy of my inheritance? I

shall give the pledge that has come ringing down the

corridors of the centuries, and it shall be compounded of the

joyous cries of my Malayan forebears when first they saw

the contours of this land loom before their eyes, of the battle

cries that have resounded in every field of combat from

Mactan to Tirad Pass, of the voices of my people when they

sing:

“I am a Filipino born to freedom, and I shall not rest until

freedom shall have been added unto my inheritance—for

myself and my children and my children’s children—

forever.”

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WORD PROBLEMS INVOLVING ANGLE OF ELEVATION AND …