1. Trigonometric Ratios
MM2G2. Students will define and
apply sine, cosine, and tangent
ratios to right triangles.
MM2G2a: Discover the relationship of
the trigonometric ratios for
similar triangles.
2. Trigonometric Ratios
MM2G2b: Explain the relationship
between the trigonometric ratios of
complementary angles.
MM2G2c: Solve application
problems using the
trigonometric ratios.
3. The following slides have been
come from the following sources:
www.mccd.edu/faculty/bruleym/.../trigonome
http://ux.brookdalecc.edu/fac/cos/lsch
melz/Math%20151/
www.scarsdaleschools.k12.ny.us /
202120915213753693/lib/…/trig.ppt
Emily Freeman
McEachern High School
4. Warm Up
Put 4 30-60-90 triangles with the following
sides listed and have students determine
the missing lengths.
30 S 5 2 7√3 √2
90 H 10 4 14√3 2√2
60 L 5√3 2√3 21 √6
5. Trigonometric Ratios
Talk about adjacent and opposite sides:
have the kids line up on the wall and
pass something from one to another
adjacent and opposite in the room.
Make a string triangle and talk about
adjacent and opposite some more
6. Trigonometric Ratios
Determine the ratios of all the triangles
on the board and realize there are only
3 (6?) different ratios.
Talk about what it means for shapes to
be similar.
Make more similar right triangles on dot
paper, measure the sides, and calculate
the ratios.
7. Trigonometric Ratios
Try to have the students measure the
angles of the triangles they made on
dot paper.
Do a Geosketch of all possible triangles
and show the ratios are the same for
similar triangles
Finally: name the ratios
8. Warm Up
Pick up a sheet of dot paper, a ruler,
and protractor from the front desk.
Draw two triangles, one with sides 3 &
4, and the other with sides 12 & 5
Calculate the hypotenuse
Calculate sine, cosine, and tangent for
the acute angles.
Measure the acute angles to the
nearest degree.
Show how to find sine, cosine, &
tangent of angles in the calculator
9. Yesterday
We learned the sine, cosine, and
tangent of the same angle of similar
triangles are the same
Another way of saying this is: The sine,
cosine, tangent of congruent angles are
the same
15. hypotenuse
leg
leg
In a right triangle, the shorter sides are called legs and the longest side
(which is the one opposite the right angle) is called the hypotenuse
a
b
c
We’ll label them a, b, and c and the angles α
and β. Trigonometric functions are defined by
taking the ratios of sides of a right triangle.
β
α
First let’s look at the three basic functions.
SINE
COSINE
TANGENT
They are abbreviated using their first 3 letters
c
a
==
hypotenuse
opposite
sinα
opposite
c
b
==
hypotenuse
adjacent
cosα
adjacent
b
a
==
adjacent
opposite
tanα
24. We could ask for the trig functions of the angle β by using the definitions.
a
b
c
You MUST get them memorized. Here is a
mnemonic to help you.
β
α
The sacred Jedi word:
SOHCAHTOA
c
b
==
hypotenuse
opposite
sin β
adjacent
cos
hypotenuse
a
c
β = = opposite
tan
adjacent
b
a
β = =
opposite
adjacent
SOHCAHTOA
25. It is important to note WHICH angle you are talking
about when you find the value of the trig function.
a
b
c
α Let's try finding some trig functions
with some numbers. Remember that
sides of a right triangle follow the
Pythagorean Theorem so
222
cba =+
Let's choose:
222
543 =+3
4
5
sin α = Use a mnemonic and
figure out which sides
of the triangle you
need for sine.
h
o
5
3
=
opposite
hypotenuse
tan β =
a
o
3
4
=
opposite
adjacent
Use a mnemonic and
figure out which sides
of the triangle you
need for tangent.
β
26. You need to pay attention to which angle you want the trig function
of so you know which side is opposite that angle and which side is
adjacent to it. The hypotenuse will always be the longest side and
will always be opposite the right angle.
α
This method only applies if you have
a right triangle and is only for the
acute angles (angles less than 90°)
in the triangle.
3
4
5
β
Oh,
I'm
acute!
So
am I!
27. We need a way
to remember
all of these
ratios…
28. What is
SohCahToa?
Is it in a tree, is it in a car, is it in the sky
or is it from the deep blue sea ?
29. This is an example of a sentence
using the word SohCahToa.
I kicked a chair in the middle of
the night and my first thought was
I need to SohCahToa.
30. An example of an acronym for SohCahToa.
Seven
old
horses
Crawled
a
hill
To
our
attic..
33. Other ways to remember SOH CAH TOA
1.Some Of Her Children Are Having Trouble
Over Algebra.
2.Some Out-Houses Can Actually Have
Totally Odorless Aromas.
3.She Offered Her Cat A Heaping Teaspoon
Of Acid.
4.Soaring Over Haiti, Courageous Amelia Hit
The Ocean And ...
5.Tom's Old Aunt Sat On Her Chair And
Hollered. -- (from Ann Azevedo)
34. Other ways to remember SOH CAH TOA
1.Stamp Out Homework Carefully, As Having
Teachers Omit Assignments.
2.Some Old Horse Caught Another Horse
Taking Oats Away.
3.Some Old Hippie Caught Another Hippie
Tripping On Apples.
4.School! Oh How Can Anyone Have Trouble
Over Academics.
37. 1.9 cm
7.7 cm
14º
1.9
7.7
≈0.25 Tangent 14º ≈0.25
The Tangent of an angle is the ratio of the
opposite side of a triangle to its adjacent side.
opposite
adjacent
hypotenuse
41. As an acute angle of a triangle
approaches 90º, its tangent
becomes infinitely large
Tan 89.9º = 573
Tan 89.99º = 5,730
Tangent A =
opposite
adjacent
etc.
very
large
very small
42. Since the sine and cosine functions always
have the hypotenuse as the denominator,
and since the hypotenuse is the longest side,
these two functions will always be less than 1.
Sine A =
opposite
hypotenuse
Cosine A =
adjacent
hypotenuse
A
Sine 89º = .9998
Sine 89.9º = .999998
45. A plane takes off from an airport an an angle of 18º and
a speed of 240 mph. Continuing at this speed and angle,
what is the altitude of the plane after 1 minute?
18º
x
After 60 sec., at 240 mph, the plane
has traveled 4 miles
4
47. An explorer is standing 14.3 miles from the base of
Mount Everest below its highest peak. His angle of
elevation to the peak is 21º. What is the number of feet
from the base of Mount Everest to its peak?
21º
x
Tan 21 =
x
14.3
0.3839 =
x
14.3
x = 5.49 miles
= 29,000 feet
1
48. A swimmer sees the top of a lighthouse on the
edge of shore at an 18º angle. The lighthouse is
150 feet high. What is the number of feet from the
swimmer to the shore?
18º
150
Tan 18 =
x
150
x
0.3249 = 150
x
0.3249x = 150
0.3249 0.3249
X = 461.7 ft1
49. A dragon sits atop a castle 60 feet high. An archer
stands 120 feet from the point on the ground directly
below the dragon. At what angle does the archer
need to aim his arrow to slay the dragon?
x
60
120
Tan x = 60
120
Tan x = 0.5
Tan-1
(0.5) = 26.6º
50. Solving a Problem with
the Tangent Ratio
60º
53 ft
h = ?
We know the angle and theWe know the angle and the
side adjacent to 60º. We want toside adjacent to 60º. We want to
know the opposite side. Use theknow the opposite side. Use the
tangent ratio:tangent ratio:
ft92353
531
3
53
60tan
≈=
=
==
h
h
h
adj
opp
1
2
3
Why?
51. A surveyor is standing 50 feet from the base
of a large tree. The surveyor measures the
angle of elevation to the top of the tree as
71.5°. How tall is the tree?
50
71.5
°
?
tan
71.5°
tan
71.5°
50
y
=
y = 50 (tan 71.5°)
y = 50 (2.98868)
149.4y ft≈
Ex.
=
Opp
Hyp
52. A person is 200 yards from a river. Rather than
walk directly to the river, the person walks along a
straight path to the river’s edge at a 60° angle.
How far must the person walk to reach the river’s
edge?
200
x
Ex. 5
60°
cos 60°
x (cos 60°) = 200
x
X = 400 yards
53.
54.
55.
56.
57.
58. Trigonometric Functions on a
Rectangular Coordinate System
x
y
θθ
Pick a point on the
terminal ray and drop a
perpendicular to the x-axis.
r
y
x
The adjacent side is x
The opposite side is y
The hypotenuse is labeled r
This is called a
REFERENCE TRIANGLE.
y
x
x
y
x
r
r
x
y
r
r
y
==
==
==
θθ
θθ
θθ
cottan
seccos
cscsin
59. Trigonometric Ratios may be found by:
45 º
1
1
2
Using ratios of special trianglesUsing ratios of special triangles
145tan
2
1
45cos
2
1
45sin
=
=
=
For angles other than 45º, 30º, 60º you will need to use aFor angles other than 45º, 30º, 60º you will need to use a
calculator. (Set it in Degree Mode for now.)calculator. (Set it in Degree Mode for now.)
