Inverse Trigonometric Functions Trigonometry MATH 103 S. Rook.
R I A N G L E. Trigonometric Ratios A RATIO is a comparison of two numbers. For example; boys to...
-
Upload
collin-mccarthy -
Category
Documents
-
view
212 -
download
0
Transcript of R I A N G L E. Trigonometric Ratios A RATIO is a comparison of two numbers. For example; boys to...
Trigonometric RatiosA RATIO is a comparison of two numbers. For example;
boys to girls cats : dogs
right : wrong.
In Trigonometry, the comparison is between
sides of a triangle.
Finding Trig Ratios
• A trigonometric ratio is a ratio of the lengths of two sides of a right triangle.
• The word trigonometry is derived from the ancient Greek language and means measurement of triangles.
• The three basic trigonometric ratios are called sine, cosine, and tangent
Some terminology:
• Before we can use the ratios we need to get a few terms straight
• The hypotenuse (hyp) is the longest side of the triangle – it never changes
• The opposite (opp) is the side directly across from the angle you are considering
• The adjacent (adj) is the side right beside the angle you are considering
A picture always helps…
• looking at the triangle in terms of angle b
AC
B
b
adjhyp
opp
b C is always the hypotenuse
A is the adjacent (near the angle)
B is the opposite (across from the angle)
LongestNear
Across
But if we switch angles…
• looking at the triangle in terms of angle a
AC
B
a
opphyp
adja
C is always the hypotenuse
A is the opposite (across from the angle)
B is the adjacent (near the angle)
LongestAcross
Near
θ this is the symbol for an unknown angle measure.
It’s name is ‘Theta’.
Don’t let it scare you… it’s like ‘x’ except for angle measure… it’s a way for us to keep our variables understandable and organized.
One more thing…
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 and . Trigonometric functions are defined by taking the ratios of sides of a right triangle.
B
A
First let’s look at the three basic functions.
SINECOSINE
TANGENT
They are abbreviated using their first 3 letters
oppositesin
hypotenuse
aA
c
opposite
adjacentcos
hypotenuse
bA
c
adjacent
oppositetan
adjacent
aA
b
the trig functions of the angle B using the definitions.
a
b
c
B
ASOHCAHTOA
oppositesin
hypotenuse
bB
c
adjacentcos
hypotenuse
aB
c
oppositetan
adjacent
bB
a
opposite
adjacent
SOHCAHTOA
hypotenuse
It is important to note WHICH angle you are talking about when you find the value of the trig function.
a
bc
A
Let's try finding some trig functions with some numbers. Remember that sides of a right triangle follow the Pythagorean Theorem so
3
45
sin A = SOH-CAH-TOAh
o5
3
opposite
hypotenuse
tan B =
a
o3
4
opposite
adjacent B
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.
A 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
45
B
Oh, I'm
acute!
So am I!
One more time…Here are the ratios:
One more time…Here are the ratios:
sinθ = opposite side hypotenuse
cosθ = adjacent side hypotenuse
tanθ =opposite side adjacent side
S OH
AHOA
C
T
SOH CAH TOA
The nice thing is that your calculator has a tan, sin and cos key that can save you some work.
However, you must remember to change the settings on your calculator from Radians to Degrees. Radians is the default setting. Here are the steps:
• Press Mode• Move the curser down to the 3rd line “Radians”• Slide the curser over so “degree” is blinking• Press 2nd Quit
Make sure you have a calculator…
Given Ratio of sides Angle, side
Looking for Angle measure Missing side
UseSIN-1
COS-1
TAN-1
SIN, COS, TAN
Calculating a side if you know the angleyou know an angle (25°) and its adjacent sidewe want to know the opposite side
adj
opptan
tan 256
A
How can we use these?
A C
B = 625°
b
.47
1 6
A
6 (.47) A
2.80 A
Another example• If you know an angle and its opposite side, you can find the adjacent side.
adj
opptan
.47 6B
A = 6 C
B 25°
b
6tan 25
B
.47 6
1 B .47 6
12.76.47 .47
B
12.76B
How can we use it?Suppose we want to find an angle
and we only know two side lengthsSuppose we want to find angle a• Is side A opposite or adjacent?
• what is side B? • with opposite and adjacent we
use the…adj
opptan
A = 3C
B = 4a
b
the opposite
the adjacent
tan ratio
Lets solve it
adj
opptan
75.04
3tan a
36.87º a
A = 3C
B = 4a
b
0.75
tana
When the tan, sin or cos is in the denominator, we are going to use the reciprocal buttons. Look above tan on the calculatorYou should see TAN-1
Press 2nd TAN (.75)
Another tangent example…
• we want to find angle b• B is the opposite• A is the adjacent• so we use tan
adj
opptan
A = 3C
B = 4
a
b
13.53
33.1tan3
4tan
b
b
b
Ex. 6: Indirect Measurement• You are measuring the height of
a Sitka spruce tree in Alaska. You stand 45 feet from the base of the tree. You measure the angle of elevation from a point on the ground to the top of the top of the tree to be 59°. To estimate the height of the tree, you can write a trigonometric ratio that involves the height h and the known length of 45 feet.
The math
tan 59° =opposite
adjacent
tan 59° =h
45
45 tan 59° = h
45 (1.6643) ≈ h
75.9 ≈ h
Write the ratio
Substitute values
Multiply each side by 45
Use a calculator or table to find tan 59°
Simplify
The tree is about 76 feet tall.
Ex. 7: Estimating Distance
• Escalators. The escalator at the Wilshire/Vermont Metro Rail Station in Los Angeles rises 76 feet at a 30° angle. To find the distance d a person travels on the escalator stairs, you can write a trigonometric ratio that involves the hypotenuse and the known leg of 76 feet.
d76 ft
30°
Now the math d76 ft
30°sin 30° =
opposite
hypotenuse
sin 30° =76
d
d sin 30° = 76
sin 30°
76d =
0.5
76d =
d = 152
Write the ratio for sine of 30°
Substitute values.
Multiply each side by d.
Divide each side by sin 30°
Substitute 0.5 for sin 30°
Simplify
A person travels 152 feet on the escalator stairs.
Why do we need the sin & cos?
• We use sin and cos when we need to work with the hypotenuse
• if you noticed, the tan formula does not have the hypotenuse in it.
• so we need different formulas to do this work• sin and cos are the ones!
C = 10A
25°
b
B
Lets do sin first
• we want to find angle a• since we have opp and hyp we use sin
hyp
oppsin
C = 10
a
b
B
A = 5
30
5.0sin10
5sin
a
a
a
And one more sin example
• find the length of side A• We have the angle and
the hyp, and we need the opp
hyp
oppsin
C = 20
25°
b
B
A 45.8
2042.0
2025sin20
25sin
A
A
A
A
And finally cos
• We use cos when we need to work with the hyp and adj
• so lets find angle bhyp
adjcos
C = 10
a
b
B
A = 4
42.66
4.0cos10
4cos
b
b
b
23.58 a
66.42 - 90 a
Here is an example• Spike wants to ride down a steel
beam• The beam is 5m long and is leaning
against a tree at an angle of 65° to the ground
• His friends want to find out how high up in the air he is when he starts so they can put add it to the doctors report at the hospital
• How high up is he?
How do we know which formula to use???
• Well, what are we working with?• We have an angle• We have hyp• We need opp• With these things we will use
the sin formula
C = 5
65°
B
So lets calculate
• so Spike will have fallen 4.53m
C = 5
65°
B
53.4
591.0
565sin5
65sin
65sin
opp
opp
opp
opp
hyp
opp
One last example…
• Lucretia drops her walkman off the Leaning Tower of Pisa when she visits Italy
• It falls to the ground 2 meters from the base of the tower
• If the tower is at an angle of 88° to the ground, how far did it fall?
First draw a triangle
• What parts do we have?• We have an angle• We have the Adjacent• We need the opposite• Since we are working with
the adj and opp, we will use the tan formula
2m
88°
B
So lets calculate
• Lucretia’s walkman fell 57.27m
2m
88°
B
27.57
264.28
288tan2
88tan
88tan
opp
opp
opp
opp
adj
opp
An application
65°
10m
You look up at an angle of 65° at the top of a tree that is 10m away
the distance to the tree is the adjacent side the height of the tree is the opposite side
4.21
14.210
65tan1010
65tan
opp
opp
opp
opp
What are the steps for doing one of these questions?
1. Make a diagram if needed2. Determine which angle you are working with3. Label the sides you are working with4. Decide which formula fits the sides5. Substitute the values into the formula6. Solve the equation for the unknown value7. Does the answer make sense?
Two Triangle Problems
• Although there are two triangles, you only need to solve one at a time
• The big thing is to analyze the system to understand what you are being given
• Consider the following problem:• You are standing on the roof of one building
looking at another building, and need to find the height of both buildings.
Draw a diagram
• You can measure the angle 40° down to the base of other building and up 60° to the top as well. You know the distance between the two buildings is 45m
60°
40°
45m
Break the problem into two triangles.
• The first triangle:
• The second triangle
• note that they share a side 45m long
• a and b are heights!
60°
45m
40°
b
a
The First Triangle
• We are dealing with an angle, the opposite and the adjacent
• this gives us Tan
60°
45m
a
77.94m a
451.73a
4560tan45
60tan
a
a
The second triangle
• We are dealing with an angle, the opposite and the adjacent
• this gives us Tan
45m
40°
b
37.76mb
450.84b
4540tan45
40tan
b
b
What does it mean?
• Look at the diagram now:• the short building is
37.76m tall• the tall building is 77.94m
plus 37.76m tall, which equals 115.70m tall
60°
40°
45m
77.94m
37.76m