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10-1Right-Angle
10-1
Right-AngleTrigonometry
Trigonometry
Warm Up
Lesson Presentation
Lesson Quiz
HoltMcDougal
Algebra 2Algebra 2
Holt
10-1 Right-Angle Trigonometry
Warm Up
Given the measure of one of the acute
angles in a right triangle, find the
measure of the other acute angle.
1. 45° 45°
2. 60° 30°
3. 24° 66°
4. 38°
Holt McDougal Algebra 2
52°
10-1 Right-Angle Trigonometry
Warm Up Continued
Find the unknown length for each right
triangle with legs a and b and hypotenuse
c.
5. b = 12, c =13
6. a = 3, b = 3
Holt McDougal Algebra 2
a=5
10-1 Right-Angle Trigonometry
Objectives
Understand and use trigonometric
relationships of acute angles in
triangles.
Determine side lengths of right
triangles by using trigonometric
functions.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Vocabulary
trigonometric function
sine
cosine
tangent
cosecants
secant
cotangent
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
A trigonometric function is a function whose
rule is given by a trigonometric ratio. A
trigonometric ratio compares the lengths of two
sides of a right triangle. The Greek letter theta θ
is traditionally used to represent the measure of
an acute angle in a right triangle. The values of
trigonometric ratios depend upon θ.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
The triangle shown at right is
similar to the one in the
table because their
corresponding angles are
congruent. No matter which
triangle is used, the value of
sin θ is the same. The values
of the sine and other
trigonometric functions
depend only on angle θ and
not on the size of the
triangle.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Example 1: Finding Trigonometric Ratios
Find the value of the
sine, cosine, and
tangent functions for θ.
sin θ =
cos θ =
tan θ =
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Check It Out! Example 1
Find the value of the
sine, cosine, and
tangent functions for θ.
sin θ =
cos θ =
tan θ =
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
You will frequently need to determine the value of
trigonometric ratios for 30°,60°, and 45° angles as
you solve trigonometry problems. Recall from
geometry that in a 30°-60°-90° triangle, the
ration of the side lengths is 1: 3 :2, and that in a
45°-45°-90° triangle, the ratio of the side lengths is
1:1: 2.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Example 2: Finding Side Lengths of Special Right
Triangles
Use a trigonometric function to find the value of x.
°
The sine function
relates the opposite
leg and the
hypotenuse.
Substitute 30° for θ, x for
opp, and 74 for hyp.
Substitute
x = 37
Holt McDougal Algebra 2
for sin 30°.
Multiply both sides by 74 to solve for x.
10-1 Right-Angle Trigonometry
Check It Out! Example 2
Use a trigonometric function to find the value of x.
°
The sine function
relates the opposite
leg and the
hypotenuse.
Substitute 45 ° for θ, x for
opp, and 20 for hyp.
Substitute
for sin 45°.
Multiply both sides by 20 to solve for x.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Example 3: Sports Application
In a waterskiing competition,
a jump ramp has the
measurements shown. To
the nearest foot, what is
the height h above water
that a skier leaves the ramp?
Substitute 15.1° for θ, h for opp., and 19
for hyp.
5≈h
Multiply both sides by 19.
Use a calculator to simplify.
The height above the water is about 5 ft.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Caution!
Make sure that your graphing calculator is set to
interpret angle values as degrees. Press
.
Check that Degree and not Radian is
highlighted in the third row.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Check It Out! Example 3
A skateboard ramp will
have a height of 12 in.,
and the angle between
the ramp and the ground
will be 17°. To the nearest inch, what will
be the length l of the ramp?
Substitute 17° for θ, l for hyp., and 12
for opp.
Multiply both sides by l and divide by
sin 17°.
Use a calculator to simplify.
l ≈ 41
The length of the ramp is about 41 in.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
When an object is above or below another object,
you can find distances indirectly by using the angle
of elevation or the angle of depression between the
objects.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Example 4: Geology Application
A biologist whose eye level is 6 ft above the
ground measures the angle of elevation to the
top of a tree to be 38.7°. If the biologist is
standing 180 ft from the tree’s base, what is
the height of the tree to the nearest foot?
Step 1 Draw and label a
diagram to represent the
information given in the
problem.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Example 4 Continued
Step 2 Let x represent the height of the tree
compared with the biologist’s eye level.
Determine the value of x.
Use the tangent function.
Substitute 38.7 for θ, x for opp., and
180 for adj.
180(tan 38.7°) = x
Multiply both sides by 180.
144 ≈ x Use a calculator to solve for x.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Example 4 Continued
Step 3 Determine the overall height of the
tree.
x + 6 = 144 + 6
= 150
The height of the tree is about 150 ft.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Check It Out! Example 4
A surveyor whose eye level is 6 ft above the
ground measures the angle of elevation to the
top of the highest hill on a roller coaster to be
60.7°. If the surveyor is standing 120 ft from
the hill’s base, what is the height of the hill to
the nearest foot?
Step 1 Draw and label a
diagram to represent the
information given in the
problem.
Holt McDougal Algebra 2
60.7°
120 ft
10-1 Right-Angle Trigonometry
Check It Out! Example 4 Continued
Step 2 Let x represent the height of the hill
compared with the surveyor’s eye level.
Determine the value of x.
Use the tangent function.
Substitute 60.7 for θ, x for opp., and
120 for adj.
120(tan 60.7°) = x
Multiply both sides by 120.
214 ≈ x Use a calculator to solve for x.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Check It Out! Example 4 Continued
Step 3 Determine the overall height of the
roller coaster hill.
x + 6 = 214 + 6
= 220
The height of the hill is about 220 ft.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
The reciprocals of the sine, cosine, and tangent
ratios are also trigonometric ratios. They are
trigonometric functions, cosecant, secant, and
cotangent.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Example 5: Finding All Trigonometric Functions
Find the values of the six trigonometric
functions for θ.
Step 1 Find the length of the hypotenuse.
a2 + b2 = c2
c2 = 242 + 702
Pythagorean Theorem.
Substitute 24 for a and
70 for b.
c2 = 5476
Simplify.
c = 74
Holt McDougal Algebra 2
Solve for c. Eliminate
the negative
solution.
70
θ
24
10-1 Right-Angle Trigonometry
Example 5 Continued
Step 2 Find the function values.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Helpful Hint
In each reciprocal pair of trigonometric functions,
there is exactly one “co”
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Check It Out! Example 5
Find the values of the six trigonometric
functions for θ.
Step 1 Find the length of the hypotenuse.
a2 + b2 = c2
c2 = 182 + 802
Pythagorean Theorem.
Substitute 18 for a and
80 for b.
c2 = 6724
Simplify.
c = 82
Holt McDougal Algebra 2
Solve for c. Eliminate
the negative
solution.
80
θ
18
10-1 Right-Angle Trigonometry
Check It Out! Example 5 Continued
Step 2 Find the function values.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Lesson Quiz: Part I
Solve each equation. Check your answer.
1. Find the values of the six trigonometric functions
for θ.
Holt McDougal Algebra 2
10-1 Right-Angle Trigonometry
Lesson Quiz: Part II
2. Use a trigonometric function to find the value
of x.
3. A helicopter’s altitude is 4500 ft, and a plane’s
altitude is 12,000 ft. If the angle of depression
from the plane to the helicopter is 27.6°, what is
the distance between the two, to the nearest
hundred feet?
16,200 ft
Holt McDougal Algebra 2