Right Triangle Trigonometry
Objectives
β’ Find trigonometric ratios using right triangles.
β’ Use trigonometric ratios to find angle measures in right triangles.
History Right triangle trigonometry is the study of the relationship between the sides and angles of right triangles. These relationships can be usedto make indirect measurements like those using similar triangles.
Trigonometric Ratios
Only Apply to Right Triangles
The 3 Trigonometric Ratios
β’ The 3 ratios are Sine, Cosine and TangentOpposite SideSine RatioHypotenuse
sin Adjacent SideCo e RatioHypotenuse
Opposite SideTangent RatioAdjacent Side
The six trigonometric functions of a right triangle, with an acute angle , are defined by ratios of two sides of the triangle. The sides of the right triangle are:
the side opposite the acute angle ,
the side adjacent to the acute angle , and the hypotenuse of the right triangle.
The trigonometric functions are sine, cosine, tangent, cotangent, secant, and cosecant.
opp
adj
hyp
ΞΈ
sin π=πππhπ¦π cosπ=
πππhπ¦π tanπ=
ππππππ
csc π=hπ¦ππππ secπ=
hπ¦ππππ cot π=
ππππππ
EVALUATING TRIGONOMETRIC FUNCTIONSπ=4 ππππ=3
Find all six trig functions of angle A
Remember SOH CAH TOA and the reciprocal identities
sin π=πππhπ¦π
cosπ=πππhπ¦π
tanπ=ππππππ
csc π=hπ¦ππππ
secπ=hπ¦ππππ
cot π=ππππππ
What is the value of h?
ΒΏπ
ΒΏπ
π45
54
35
53
43
34
EVALUATING TRIGONOMETRIC FUNCTIONSπ=12ππππ=5
Find all six trig functions of angle A
Remember SOH CAH TOA and the reciprocal identities
sin π=πππhπ¦π
cosπ=πππhπ¦π
tanπ=ππππππ
csc π=hπ¦ππππ
secπ=hπ¦ππππ
cot π=ππππππ
What is the value of h?
ΒΏππ
ΒΏπ
ππ1213
1312
513
135
125
512
EVALUATING TRIGONOMETRIC FUNCTIONSπ=1πππ h=3
Find all six trig functions of angle A
Remember SOH CAH TOA and the reciprocal identities
sin π=πππhπ¦π
cosπ=πππhπ¦π
tanπ=ππππππ
csc π=hπ¦ππππ
secπ=hπ¦ππππ
cot π=ππππππ
What is the value of b?
ΒΏπ
ΒΏπβπ
π13 3
2β23
3β24
β24
2β2
Calculate the trigonometric functions for a 45 angle.
2
1
1
45
csc 45 = = =
12 2
opphypsec 45 = = =
12 2
adjhyp
cos 45 = = =
22
21
hypadjsin 45 = = =
22
21
hypopp
cot 45 = = = 1
oppadj
11tan 45 = = = 1
adjopp
11
60β 60β
Consider an equilateral triangle with each side of length 2.
The perpendicular bisector
of the base bisects the opposite angle.
The three sides are equal, so the angles are equal; each is 60.
Geometry of the 30-60-90 triangle
2 2
21 1
30β 30β
3
Use the Pythagorean Theorem to find the length of the altitude, .
Calculate the trigonometric functions for a 30 angle.
12
303
sin 30 Β°=πππhπ¦π =
12
cos 30 Β°= πππhπ¦π=β3
2
tan 30 Β°=ππππππ = 1
β3=β3
3 cot 30 Β°= πππhπ¦π=β3
1=β3
sec 30Β°=hπ¦ππππ =2β3
=2β33
csc 30 Β°= hπ¦ππππ=21=2
Calculate the trigonometric functions for a 60 angle.
12 60
3
sin 60 Β°=πππhπ¦π =β3
2
cos 60 Β°= πππhπ¦π=
12
tan 60 Β°=ππππππ =β3
1=β3 cot 60 Β°= πππ
hπ¦π= 1β3
=β33
sec 60Β°=hπ¦ππππ =21=2
csc 60 Β°= hπ¦ππππ= 2β3
=2β33
TRIG FUNCTIONS & COMPLEMENTSTwo positive angles are complements if the sum of their measures is .
Example: are complement because .
The sum of the measures of the angles in a triangle is . In a right triangle, we have a angle. That means that the sum of the other two angles is . Those two angles are acute and complement.
If the degree measure of one acute angle is , then the degree measure of the other angle is .
TRIG FUNCTIONS & COMPLEMENTSCompare and .
Therefore, . If two angles are complements, the sine of one equals the cosine of the other.
sin π=cos ( π2 βπ) cosπ=sin ( π2 βπ)
tanπ=co t (π2 βπ) cot π= tan ( π2 βπ)
secπ=csc (π2 βπ) csc π=π ππ (π2 βπ)
Using cofunction identitiesFind a cofunction with the same value as the given expression:
Find a cofunction with the same value as the given expression:
ΒΏ sec ( π2 βπ3 )
An angle formed by a horizontal line and the line of sight to an object that is above the horizontal line is called the angle of elevation. The angle formedby a horizontal line and the line of sight to an objectthat is below the horizontal line is called the angle ofdepression. Transits and sextants are instrumentsused to measure such angles.
Angle of Elevation
Angle of Depression
Angle of ELEVATION AND DEPRESSION
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 71.5Β°. How tall is the tree?
50
71.5Β°
?
tan 71.5Β°
tan 71.5Β°50y
y = 50 (tan 71.5Β°) y = 50 (2.98868) 149.4y ft
OppAdj
Look at the given info. What trig function can we use?
A person is 200 yards from a river. Rather than walk directly to the river, the person walks along a straight path to the riverβs edge at a 60Β° angle. How far must the person walk to reach the riverβs edge?
200x
60Β°
cos 60Β°
x (cos 60Β°) = 200
x
X = 400 yardsLook at the given information. Which trig function should we use?
570tan 0 x
h = (13.74 + 2) meters
A guy wire from a point 2 m from the top of an electric post makes an angle of 700 with the ground. If the guy wire is anchored 5 m from the base of the post, how high is the pole?
5 m
700
2 m
Guy wire
h = 15.74 meters
x
Which trig function should we use?
Great job, you guys!