1. Trigonometry
By Nittaya Noinan
Kanchanapisekwittayalai phetchabun school
Grade 10

2. Trigonometry
 Trigonometry is derived from Greek words
trigonon (three angles) and metron ( measure).
 Trigonometry is the branch of mathematics
which deals with triangles, particularly triangles
in a plane where one angle of the triangle is 90
degrees
 Triangles on a sphere are also studied, in
spherical trigonometry.
 Trigonometry specifically deals with the
relationships between the sides and the angles of
triangles, that is, on the trigonometric functions,
and with calculations based on these functions.

3. History
 The origins of trigonometry can be traced to the civilizations
of ancient Egypt, Mesopotamia and the Indus Valley, more
than 4000 years ago.
 Some experts believe that trigonometry was originally
invented to calculate sundials, a traditional exercise in the
oldest books
 The first recorded use of trigonometry came from the
Hellenistic mathematician Hipparchus circa 150 BC, who
compiled a trigonometric table using the sine for solving
triangles.
 The Sulba Sutras written in India, between 800 BC and 500
BC, correctly compute the sine of π/4 (45°) as 1/√2 in a
procedure for circling the square (the opposite of squaring the
circle).
 Many ancient mathematicians like Aryabhata,
Brahmagupta,Ibn Yunus and Al-Kashi made significant
contributions in this field(trigonometry).

4. Right Triangle
 A triangle in which one angle
is equal to 90° is called right
triangle.
 The side opposite to the right
angle is known as hypotenuse.
AB is the hypotenuse
 The other two sides are
known as legs.
AC and BC are the legs
Trigonometry deals with Right Triangles

5. Pythagoras Theorem
In any right triangle, the area of the square whose
side is the hypotenuse is equal to the sum of areas of
the squares whose sides are the two legs.
In the figure
AB2 = BC2 + AC2

6. Unit Circle
A Unit Circle Is a Circle With Radius Equals to 1
Unit.(We Always Choose Origin As Its centre)
Y
1 units
x

7. Trigonometry
Trigonometry is the branch of mathematics that looks
at the relationship between the length of the sides
and the angles in a right angled triangle.
It helps us calculate the length of unknown sides,
without drawing the triangle, and it also helps us
calculate the size of an unknown angle without having
to measure it.
Let us look at a right angle triangle.

8. Trigonometry
C
Hypotenuse Opposite
The ‘Hypotenuse’ is always
x0 opposite the right angle
O Adjacent F The ‘Opposite’ is always
opposite the angle under
investigation.
C The ‘Adjacent’ is always
alongside the angle under
y0 investigation.
Hypotenuse
Adjacent
O F
Opposite

9. Trigonometry
C
Let us look at the
3 ratio or fraction of
the opposite over
the adjacent.
270
O 6 F
CF 3 1
= = Let us now split this triangle up.
OF 6 2

10. Trigonometry
C
B Let us look at the
3 ratio or fraction of
2 the opposite over
the adjacent
270
O 4 E 2 F
CF 3 1
= =
OF 6 2 Let us split it again.
BE 2 1
= =
OE 4 2

11. Adjacent , Opposite Side and
Hypotenuse of a Right Angle Triangle.

12. se
nu
θ
te
po Adjacent side
hy
Opposite side

13. se
nu
te
po
Opposite side
hy
φ
Adjacent side

14. Three Types Trigonometric Ratios
There are 3 kinds of trigonometric
ratios we will learn.
sine ratio
cosine ratio
tangent ratio

15. Sine Ratios
 Definition of Sine Ratio.
 Application of Sine Ratio.

16. Definition of Sine Ratio.
1
θ
If the hypotenuse equals to 1
Sinθ = Opposite sides

17. Definition of Sine Ratio.
θ
For any right-angled triangle
Opposite side
Sinθ =
hypotenuses

18. Exercise 1
In the figure, find sin θ θ
Opposite Side 4
Sinθ = 7
hypotenuses
4
=
7
θ= 34.85° (corr to 2 d.p.)

19. Exercise 2
In the figure, find y
y
Opposite Side
Sin35° =
hypotenuses
35° 11
y
Sin35° =
11
y= 11 sin35°
y= 6.31 (corr to 2.d.p.)

20. Cosine Ratios
 Definition of Cosine.
 Relation of Cosine to the sides of right
angle triangle.

21. Definition of Cosine Ratio.
1
θ
If the hypotenuse equals to 1
Cosθ = Adjacent Side

22. Definition of Cosine Ratio.
θ
For any right-angled triangle
Adjacent Side
Cosθ =
hypotenuses

23. Exercise 3
3
In the figure, find cos θ θ
adjacent Side
cosθ = 8
hypotenuses
3
=
8
θ= 67.98° (corr to 2 d.p.)

24. Exercise 4
In the figure, find x
6
Adjacent Side
Cos 42° =
42°
hypotenuses
x
6
Cos 42° = x
6
x=
Cos 42°
x= 8.07 (corr to 2.d.p.)

25. Tangent Ratios
 Definition of Tangent.
 Relation of Tangent to the sides of right
angle triangle.

26. Definition of Tangent Ratio.
θ
For any right-angled triangle
Opposite Side
tanθ =
Adjacent Side

27. Exercise 5
3
In the figure, find tan θ
Opposite side 5
tanθ =
adjacent Side
θ
3
=
5
θ= 78.69° (corr to 2 d.p.)

28. Exercise 6
In the figure, find z
z
22°
Opposite side
tan 22° =
adjacent Side
5
5
tan 22° =
z
5
z=
tan 22°
z= 12.38 (corr to 2 d.p.)

29. Conclusion
opposite side
sin θ =
hypotenuse
Make Sure
adjacent side that the
cos θ = triangle is
hypotenuse right-angled
opposite side
tan θ =
adjacent side

30. Trigonometric ratios
 Sine(sin) opposite side/hypotenuse
 Cosine(cos) adjacent side/hypotenuse
 Tangent(tan) opposite side/adjacent side
 Cosecant(cosec) hypotenuse/opposite side
 Secant(sec) hypotenuse/adjacent side
 Cotangent(cot) adjacent side/opposite side
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31. Values of trigonometric function
of Angle A
sinθ = a/c
cosθ = b/c
tanθ = a/b
cosecθ = c/a
secθ = c/b
cotθ = b/a 31

32. Values of Trigonometric function
0 30 45 60 90
Sine 0 0.5 1/√2 √3/2 1
Cosine 1 √3/2 1/√2 0.5 0
Tangent 0 1/ √3 1 √3 Not defined
Not
Cosecant 2 √2 2/ √3 1
defined
Secant 1 2/ √3 √2 2 Not defined
Not
Cotangent √3 1 1/ √3 0
defined
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33. Calculator
 This Calculates the values of trigonometric functions of
different angles.
 First Enter whether you want to enter the angle in
radians or in degrees. Radian gives a bit more accurate
value than Degree.
 Then Enter the required trigonometric function in the
format given below:
 Enter 1 for sin.
 Enter 2 for cosine.
 Enter 3 for tangent.
 Enter 4 for cosecant.
 Enter 5 for secant.
 Enter 6 for cotangent.
 Then enter the magnitude of angle.
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34. Trigonometric identities
 sin2A + cos2A = 1
 1 + tan2A = sec2A
 1 + cot2A = cosec2A
 sin(A+B) = sinAcosB + cosAsin B
 cos(A+B) = cosAcosB – sinAsinB
 tan(A+B) = (tanA+tanB)/(1 – tanAtan B)
 sin(A-B) = sinAcosB – cosAsinB
 cos(A-B)=cosAcosB+sinAsinB
 tan(A-B)=(tanA-tanB)(1+tanAtanB)
 sin2A =2sinAcosA
 cos2A=cos2A - sin2A
 tan2A=2tanA/(1-tan2A)
 sin(A/2) = ±√{(1-cosA)/2}
 Cos(A/2)= ±√{(1+cosA)/2}
 Tan(A/2)= ±√{(1-cosA)/(1+cosA)} 34

35. Relation between different
Trigonometric Identities
 Sine
 Cosine
 Tangent
 Cosecant
 Secant
 Cotangent
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36. Angles of Elevation and
Depression
 Line of sight: The line from our eyes to the
object, we are viewing.
 Angle of Elevation:The angle through which
our eyes move upwards to see an object
above us.
 Angle of depression:The angle through
which our eyes move downwards to see an
object below us.
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37. Problem solved using
trigonometric ratios
CLICK HERE!
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38. Applications of Trigonometry
 This field of mathematics can be applied in astronomy,navigation,
music theory, acoustics, optics, analysis of financial markets,
electronics, probability theory, statistics, biology, medical imaging
(CAT scans and ultrasound), pharmacy, chemistry, number theory
(and hence cryptology), seismology, meteorology, oceanography,
many physical sciences, land surveying and geodesy, architecture,
phonetics, economics, electrical engineering, mechanical engineering,
civil engineering, computer graphics, cartography, crystallography and
game development.
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39. Derivations
 Most Derivations heavily rely on
Trigonometry.
Click the hyperlinks to view the derivation
 A few such derivations are given below:-
 Parallelogram law of addition of vectors.
 Centripetal Acceleration.
 Lens Formula
 Variation of Acceleration due to gravity due
to rotation of earth.
 Finding angle between resultant and the
vector.
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40. Applications of Trigonometry in
Astronomy
 Since ancient times trigonometry was used in astronomy.
 The technique of triangulation is used to measure the distance to nearby stars.
 In 240 B.C., a mathematician named Eratosthenes discovered the radius of the
Earth using trigonometry and geometry.
 In 2001, a group of European astronomers did an experiment that started in 1997
about the distance of Venus from the Sun. Venus was about 105,000,000
kilometers away from the Sun .
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41. Application of Trigonometry in
Architecture
 Many modern buildings have beautifully curved surfaces.
 Making these curves out of steel, stone, concrete or glass is
extremely difficult, if not impossible.
 One way around to address this problem is to piece the
surface together out of many flat panels, each sitting at an
angle to the one next to it, so that all together they create
what looks like a curved surface.
 The more regular these shapes, the easier the building
process.
 Regular flat shapes like squares, pentagons and hexagons,
can be made out of triangles, and so trigonometry plays an
important role in architecture.
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42. Waves
 The graphs of the functions sin(x) and cos(x) look like waves. Sound
travels in waves, although these are not necessarily as regular as those
of the sine and cosine functions.
 However, a few hundred years ago, mathematicians realized that any
wave at all is made up of sine and cosine waves. This fact lies at the
heart of computer music.
 Since a computer cannot listen to music as we do, the only way to get
music into a computer is to represent it mathematically by its
constituent sound waves.
 This is why sound engineers, those who research and develop the
newest advances in computer music technology, and sometimes even
composers have to understand the basic laws of trigonometry.
 Waves move across the oceans, earthquakes produce shock waves and
light can be thought of as traveling in waves. This is why trigonometry
is also used in oceanography, seismology, optics and many other fields
like meteorology and the physical sciences.
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43. Digital Imaging
 In theory, the computer needs an infinite amount of information to do
this: it needs to know the precise location and colour of each of the
infinitely many points on the image to be produced. In practice, this is
of course impossible, a computer can only store a finite amount of
information.
 To make the image as detailed and accurate as possible, computer
graphic designers resort to a technique called triangulation.
 As in the architecture example given, they approximate the image by a
large number of triangles, so the computer only needs to store a finite
amount of data.
 The edges of these triangles form what looks like a wire frame of the
object in the image. Using this wire frame, it is also possible to make
the object move realistically.
 Digital imaging is also used extensively in medicine, for example in
CAT and MRI scans. Again, triangulation is used to build accurate
images from a finite amount of information.
 It is also used to build "maps" of things like tumors, which help decide
how x-rays should be fired at it in order to destroy it.
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44. Conclusion
Trigonometry is a branch of Mathematics with
several important and useful applications.
Hence it attracts more and more research with
several theories published year after year
Thank You
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45. END