MAHIP

SINGH

X-B

SOME APPLICATION OF TRIGNOMETRY

INTRODUCTION• TRIGONOMETRY IS THE BRANCH OF MATHEMATICS THAT

DEALS WITH TRIANGLES PARTICULARLY RIGHT TRIANGLES. FOR ONE THING TRIGONOMETRY WORKS WITH ALL ANGLES AND NOT JUST TRIANGLES. THEY ARE BEHIND HOW SOUND AND LIGHT MOVE AND ARE ALSO INVOLVED IN OUR PERCEPTIONS OF BEAUTY AND OTHER FACETS ON HOW OUR MIND WORKS. SO TRIGONOMETRY TURNS OUT TO BE THE FUNDAMENTAL TO PRETTY MUCH EVERYTHING

BASIC FUNDAMENTALS• ANGLE OF ELEVATION: IN THE PICTURE BELOW,

AN OBSERVER IS STANDING AT THE TOP OF A BUILDING IS LOOKING STRAIGHT AHEAD (HORIZONTAL LINE). THE OBSERVER MUST RAISE HIS EYES TO SEE THE AIRPLANE (SLANTING LINE). THIS IS KNOWN AS THE ANGLE OF ELEVATION.

• ANGLE OF DEPRESSION: THE ANGLE BELOW HORIZONTAL THAT AN OBSERVER MUST LOOK TO SEE AN OBJECT THAT IS LOWER THAN THE OBSERVER. NOTE: THE ANGLE OF DEPRESSION IS CONGRUENT TO THE ANGLE OF ELEVATION (THIS ASSUMES THE OBJECT IS CLOSE ENOUGH TO THE OBSERVER SO THAT THE HORIZONTALS FOR THE OBSERVER AND THE OBJECT ARE EFFECTIVELY PARALLEL).

600

300

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If θ is an angleThe 90-θ is it’s complimentary angle

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Tan

Cos

Sine

A trigonometric function is a ratio of certain parts of a triangle. The names of these ratios are: The sine, cosine, tangent, cosecant, secant, cotangent.

Let us look at this triangle…

ac

bө A

B

C

Given the assigned letters to the sides and angles, we can determine the following

trigonometric functions.

The Cosecant is the inversion of the sine, the secant is the inversion of

the cosine, the cotangent is the inversion of the tangent.

With this, we can find the sine of the value of angle A by dividing side a by side c. In order to find the angle itself, we must take the sine of the angle and invert it (in other words, find the cosecant of the sine of the angle).

Sinθ=

Cos θ=

Tan θ=

Side Opposite

Side Adjacent

Side AdjacentSide Opposite

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cBY- MAHIP SINGH X-BBY-MAHIP SINGH X-B

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The angle of elevation of the top of a tower from a point At the foot of the tower is 300 . And after advancing 150mtrs Towards the foot of the tower, the angle of elevation becomes 600 .Find the height of the tower

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How the following diagram allows us to determine the height of the Eiffel Tower without actually having to climb it or the distance between the person and Eiffel Tower without actually walking .

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Heights and Distances

In this situation , the distance or the heights can be founded by using mathematical techniques, which comes under a branch of ‘trigonometry’. The word ‘ trigonometry’ is derived from the Greek word ‘tri’ meaning three , ‘gon’ meaning sides and ‘metron’ meaning measures. Trigonometry is concerned with the relationship between the angles and sides of triangles. An understanding of these relationships enables unknown angles and sides to be calculated without recourse to direct measurement. Applications include finding heights/distances of objects.

Early Beginning uses of trigonometry for determining heights and distances

Trigonometry (Three-angle-measure)

THE GREAT PYRAMID (CHEOPS) AT GIZA, NEAR CAIRO, ONE OF THE 7 WONDERS OF THE ANCIENT WORD. (THE ONLY ONE STILL SURVIVING).THIS IS THE ONE OF THE EARLIEST USE OF TRIGONOMETRY. PEOPLE USE TRIGONOMETRY FOR DETERMINING HEIGHT OF THIS PYRAMID.

Sun’s rays casting shadows mid-afternoon

Sun’s rays casting shadows late afternoon

An early application of trigonometry was made by Thales on a visit to Egypt. He was surprised that no one could tell him the height of the 2000 year old Cheops pyramid. He used his knowledge of the relationship between the heights of objects and the length of their shadows to calculate the height for them. (This will later become the Tangent ratio.) Can you see what this relationship is, based on the drawings below?

Thales of Miletus 640 – 546 B.C. The

first Greek Mathematician. He predicted the Solar Eclipse of 585 BC.

Trigonometry

Similar Triangles

Similar Triangles

Thales may not have used similar triangles directly to solve the problem but he knew that the ratio of the vertical to horizontal sides of each triangle was constant and unchanging for different heights of the sun. Can you use the measurements shown above to find the height of Cheops?

6 ft9 ft

720 fth

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480 ft

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Early Applications of TrigonometryFinding the height of a mountain/hill.

Finding the distance to the moon.

Constructing sundials to estimate the time from the sun’s shadow.

Historically trigonometry was developed for work in Astronomy and Geography. Today it is used extensively in mathematics and many other areas of the sciences.• Surveying• Navigation• Physics• Engineering

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Angle of elevation

Line of sight

A

C

B

In this figure, the line AC drawn from the eye of the student to the top of the tower is called the line of sight. The person is looking at the top of the tower. The angle BAC, so formed by line of sight with horizontal is called angle of elevation.

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Angles. of Elevation and Depression

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In this figure, the person standing on the top of the mountain is looking down at a flower pot. In this case , the line of sight is below the horizontal level. The angle so formed by the line of sight with the horizontal is called the angle of depression.

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Line of si

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Method of finding the heights or the distances

Let us refer to figure of tower again. If you want to find the height of the tower i.e. BC without actually measuring it, what information do you need ?

We would need to know the following: i. The distance AB which is the distance

between tower and the person .ii. The angle of elevation angle BAC .Assuming that the above two conditions are given then how can we determine the height of the height of the tower ? In ∆ABC, the side BC is the opposite side in relation to the known angle A. Now, which of the trigonometric ratios can we use ? Which one of them has the two values that we have and the one we need to determine ? Our search narrows down to using either tan A or cot A, as these ratios involve AB and BC. Therefore, tan A = BC/AB or cot A = AB/BC, which on solving would give us BC i.e., the height of the tower.

The angle of elevation of the top of a tower from a point At the foot of the tower is 300 . And after advancing 150mtrs Towards the foot of the tower, the angle of elevation becomes 600 .Find the height of the tower

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I see a bird flying at a constant speed of 1.7568 kmph in the sky. The angle of elevation is 600. After ½ a minute, I see the bird again and the angle of elevation is 450. The perpendicular distance of the bird from me, now will be(horizontal distance) ?

ANSWER : Let A be the initial position and B be the final position of the bird, <AED= 600 , <BED = 450

Let E be my position. Time required to cover distance from A to B=30 sec.

Speed of bird= 1.7568 × m/s

Distance travelled by bird in 30 sec. = 1.7568 × × 30 = 14.64 m

In right angled = Tan 600 . Thus, ED =

In right angled As EC=ED+DC ,,, BC= +DC ,,, BC= + 14.64

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Thank you

BY- MAHIP SINGH X-BX-B