Elementary Geometry For College Students, 7e
7th Edition
ISBN:9781337614085
Author:Alexander, Daniel C.; Koeberlein, Geralyn M.
Publisher:Alexander, Daniel C.; Koeberlein, Geralyn M.
ChapterP: Preliminary Concepts
SectionP.CT: Test
Problem 1CT
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![**Trigonometry Problem: Using the Law of Cosines to Find an Angle**
In the given triangle \( \Delta RST \), the side lengths are as follows: \( r = 3.9 \) inches, \( s = 5.6 \) inches, and \( t = 6.1 \) inches.
To find the measure of angle \( \angle S \) to the nearest 10th degree, you can use the Law of Cosines formula:
\[ c^2 = a^2 + b^2 - 2ab \cdot \cos(C) \]
Where \( a \), \( b \), and \( c \) are the sides of the triangle, and \( C \) is the angle opposite side \( c \).
**Step-by-Step Solution:**
1. Identify the sides opposite to the angles:
- In this case, let side \( r \) be opposite angle \( \angle R \),
- side \( s \) be opposite angle \( \angle S \),
- and side \( t \) be opposite angle \( \angle T \).
2. Rewrite the Law of Cosines for finding \( \angle S \):
\[ s^2 = r^2 + t^2 - 2rt \cdot \cos(S) \]
3. Substitute the known values:
\[ 5.6^2 = 3.9^2 + 6.1^2 - 2 \cdot 3.9 \cdot 6.1 \cdot \cos(S) \]
4. Calculate each term:
\[ 31.36 = 15.21 + 37.21 - 2 \cdot 3.9 \cdot 6.1 \cdot \cos(S) \]
\[ 31.36 = 52.42 - 47.58 \cdot \cos(S) \]
5. Isolate \( \cos(S) \):
\[ 31.36 - 52.42 = - 47.58 \cdot \cos(S) \]
\[ -21.06 = - 47.58 \cdot \cos(S) \]
\[ \cos(S) = \frac{21.06}{47.58} \]
\[ \cos(S) \approx 0.4427 \](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F9e9625c3-924e-4709-97fa-b0ab1da65dbe%2F369090ad-82e1-4407-bf85-69b439d3312f%2Fzsc113c_processed.jpeg&w=3840&q=75)
Transcribed Image Text:**Trigonometry Problem: Using the Law of Cosines to Find an Angle**
In the given triangle \( \Delta RST \), the side lengths are as follows: \( r = 3.9 \) inches, \( s = 5.6 \) inches, and \( t = 6.1 \) inches.
To find the measure of angle \( \angle S \) to the nearest 10th degree, you can use the Law of Cosines formula:
\[ c^2 = a^2 + b^2 - 2ab \cdot \cos(C) \]
Where \( a \), \( b \), and \( c \) are the sides of the triangle, and \( C \) is the angle opposite side \( c \).
**Step-by-Step Solution:**
1. Identify the sides opposite to the angles:
- In this case, let side \( r \) be opposite angle \( \angle R \),
- side \( s \) be opposite angle \( \angle S \),
- and side \( t \) be opposite angle \( \angle T \).
2. Rewrite the Law of Cosines for finding \( \angle S \):
\[ s^2 = r^2 + t^2 - 2rt \cdot \cos(S) \]
3. Substitute the known values:
\[ 5.6^2 = 3.9^2 + 6.1^2 - 2 \cdot 3.9 \cdot 6.1 \cdot \cos(S) \]
4. Calculate each term:
\[ 31.36 = 15.21 + 37.21 - 2 \cdot 3.9 \cdot 6.1 \cdot \cos(S) \]
\[ 31.36 = 52.42 - 47.58 \cdot \cos(S) \]
5. Isolate \( \cos(S) \):
\[ 31.36 - 52.42 = - 47.58 \cdot \cos(S) \]
\[ -21.06 = - 47.58 \cdot \cos(S) \]
\[ \cos(S) = \frac{21.06}{47.58} \]
\[ \cos(S) \approx 0.4427 \
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