SECTION 4.1 Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 345
Chapter 4 Trigonometric Functions
Section 4.1: Special Right Triangles and
Trigonometric Ratios
Special Right Triangles
Trigonometric Ratios
Special Right Triangles
Right Triangles:
CHAPTER 4 Trigonometric Functions
University of Houston Department of Mathematics 346
45o-45o-90o Triangles:
Theorem for 45o-45
o-90
o Triangles:
Example:
Solution:
SECTION 4.1 Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 347
30o-60o-90o Triangles:
Theorem for 30o-60
o-90
o Triangles:
Example:
CHAPTER 4 Trigonometric Functions
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Solution:
Additional Example 1:
Solution:
Part (a):
Part (b):
SECTION 4.1 Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 349
Additional Example 2:
Solution:
CHAPTER 4 Trigonometric Functions
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Additional Example 3:
Solution:
Part (a):
Part (b):
SECTION 4.1 Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 351
Additional Example 4:
Solution:
CHAPTER 4 Trigonometric Functions
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Additional Example 5:
Solution:
SECTION 4.1 Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 353
Trigonometric Ratios
The Three Basic Trigonometric Ratios:
Example:
CHAPTER 4 Trigonometric Functions
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Solution:
SECTION 4.1 Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 355
The Three Reciprocal Trigonometric Ratios:
CHAPTER 4 Trigonometric Functions
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Example:
Solution:
SECTION 4.1 Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 357
Additional Example 1:
Solution:
Part (a):
Part (b):
CHAPTER 4 Trigonometric Functions
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Part (c):
Additional Example 2:
SECTION 4.1 Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 359
Solution:
CHAPTER 4 Trigonometric Functions
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Additional Example 3:
Solution:
SECTION 4.1 Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 361
Additional Example 4:
Solution:
CHAPTER 4 Trigonometric Functions
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Exercise Set 4.1: Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 363
45o
8
x
Answer the following.
1. If two sides of a triangle are congruent, then the
__________ opposite those sides are also
congruent.
2. If two angles of a triangle are congruent, then the
__________ opposite those angles are also
congruent.
3. In any triangle, the sum of the measures of its
angles is _____ degrees.
4. In an isosceles right triangle, each acute angle
measures _____ degrees.
5. Fill in each missing blank with one of the
following: smallest, largest
In any triangle, the longest side is opposite the
__________ angle, and the shortest side is
opposite the __________ angle.
6. Fill in each missing blank with one of the
following: 30o, 60o, 90o
In a 30o-60o-90o triangle, the hypotenuse is
opposite the _____ angle, the shorter leg is
opposite the _____ angle, and the longer leg is
opposite the _____ angle.
For each of the following,
(a) Use the theorem for 45o-45
o-90
o triangles to
find x.
(b) Use the Pythagorean Theorem to verify the
result obtained in part (a).
7.
8.
9.
10.
11.
12.
13.
14.
15.
45o
5
x
45o
8
x
45o
x
4 2
45o
x
3 2
45o
x
8
45o
x
7
9
x
12 x
45o
x
4 2
45o
x
4 2
x
8 2
Exercise Set 4.1: Special Right Triangles and Trigonometric Ratios
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16.
17.
18.
The following examples help to illustrate the theorem
regarding 30o-60
o-90
o triangles.
19. What is the measure of each angle of an
equilateral triangle?
20. An altitude is drawn to the base of the equilateral
triangle drawn below. Find the measures of x and
y.
21. In the figure below, an altitude is drawn to the
base of an equilateral triangle.
(a) Find a and b.
(b) Justify the answer obtained in part (a).
(c) Use the Pythagorean Theorem to find c, the
length of the altitude.
22. In the figure below, an altitude is drawn to the
base of an equilateral triangle.
(a) Find a and b.
(b) Justify the answer obtained in part (a).
(c) Use the Pythagorean Theorem to find c, the
length of the altitude. (Write c in simplest
radical form.)
For each of the following, Use the theorem for 30o-60
o-
90o triangles to find x and y.
23.
24.
25.
26.
yo
xo
30o
30o
a b
10
c
60o 60o
30o
30o
a b
4
c
60o 60o
30o
x
y
7
30o
22
y
x
30o
x
8
y
60o
x
y
6 3
45o
2 3
x
45o
x
2 3
x
5 2
Exercise Set 4.1: Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 365
27.
28.
29.
30.
31.
32.
Answer the following. Write answers in simplest form.
33.
(a) Use the Pythagorean Theorem to find BC.
(b) Find the following:
sin _____A sin _____B
cos _____A cos _____B
tan _____A tan _____B
34.
(a) Use the Pythagorean Theorem to find DE.
(b) Find the following:
sin _____D sin _____F
cos _____D cos _____F
tan _____D tan _____F
35. Suppose that is an acute angle of a right
triangle and 5
sin7
. Find cos and
tan .
36. Suppose that is an acute angle of a right
triangle and 4 2
tan7
. Find sin and
cos .
37. The reciprocal of the sine function is the
_______________ function.
38. The reciprocal of the cosine function is the
_______________ function.
39. The reciprocal of the tangent function is the
_______________ function.
40. The reciprocal of the cosecant function is the
_______________ function.
41. The reciprocal of the secant function is the
_______________ function.
42. The reciprocal of the cotangent function is the
_______________ function.
60o
x
y
5
60o
y
15 3
x
30o
x
6
y
x
30o
8
y
60o
x
y
4 2
60o
y 5 3
x
24
25 D
F E
15 17
A
B C
Exercise Set 4.1: Special Right Triangles and Trigonometric Ratios
University of Houston Department of Mathematics 366
43.
(a) Use the Pythagorean Theorem to find x.
(b) Find the six trigonometric functions of .
(c) Find the six trigonometric functions of .
44.
(a) Use the Pythagorean Theorem to find x.
(b) Find the six trigonometric functions of .
(c) Find the six trigonometric functions of .
45.
(a) Use the Pythagorean Theorem to find x.
(b) Find the six trigonometric functions of .
(c) Find the six trigonometric functions of .
46.
(a) Use the Pythagorean Theorem to find x.
(b) Find the six trigonometric functions of .
(c) Find the six trigonometric functions of .
47. Suppose that is an acute angle of a right
triangle and 2 10
cot3
. Find the six
trigonometric functions of .
48. Suppose that is an acute angle of a right
triangle and 5
sec2
. Find the six
trigonometric functions of .
49.
(a) Use the theorems for special right triangles
to find the missing side lengths in the
triangles above.
(b) Using the triangles above, find the
following:
sin 45 _____ csc 45 _____
cos 45 _____ sec 45 _____
tan 45 _____ cot 45 _____
(c) Using the triangles above, find the
following:
sin 30 _____ csc 30 _____
cos 30 _____ sec 30 _____
tan 30 _____ cot 30 _____
(d) Using the triangles above, find the
following:
sin 60 _____ csc 60 _____
cos 60 _____ sec 60 _____
tan 60 _____ cot 60 _____
6
x
5
8
x 4
8
x
6
x
7
4
45o
3
60o
30o
2
Exercise Set 4.1: Special Right Triangles and Trigonometric Ratios
MATH 1330 Precalculus 367
50.
(a) Use the theorems for special right triangles
to find the missing side lengths in the
triangles above.
(b) Using the triangles above, find the
following:
sin 45 _____ csc 45 _____
cos 45 _____ sec 45 _____
tan 45 _____ cot 45 _____
(c) Using the triangles above, find the
following:
sin 30 _____ csc 30 _____
cos 30 _____ sec 30 _____
tan 30 _____ cot 30 _____
(d) Using the triangles above, find the
following:
sin 60 _____ csc 60 _____
cos 60 _____ sec 60 _____
tan 60 _____ cot 60 _____
51. Compare the answers to parts (b), (c), and (d) in
the previous two examples. What do you notice?
45o
8
60o
30o
12
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