B C. a A b c = 15 and mZB= 78°. Find a.

Elementary Geometry For College Students, 7e
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ISBN:9781337614085
Author:Alexander, Daniel C.; Koeberlein, Geralyn M.
Publisher:Alexander, Daniel C.; Koeberlein, Geralyn M.
ChapterP: Preliminary Concepts
SectionP.CT: Test
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### Problem Statement:

In the given right-angled triangle ΔABC, angle ∠C is 90°. The vertices are labeled as follows:
- A at the left-most point,
- B at the top-right point, and
- C at the bottom-right point where the right angle is formed.

The sides of the triangle are designated as:
- Side opposite to angle A (between B and C) is 'a',
- Side adjacent to angle A (between A and C) is 'b',
- Hypotenuse (between A and B) is 'c'.

Given:
- Length of the hypotenuse, c = 15 units
- Measure of angle ∠B = 78°

Question:
- Find the length of side 'a'.

### Diagram:

Here we have a right-angled triangle with:
- Right angle at C (∠C = 90°)
- Hypotenuse (c) connecting points A and B
- Vertical side (a) connecting points B and C
- Horizontal side (b) connecting points A and C.

### Solution:

To find the length of side 'a', we utilize trigonometric relationships in the right-angled triangle. 

Given that:
- \( c = 15 \)
- \( \angle B = 78° \)

To find side 'a', observe that in triangle ΔABC:
\[
\sin(\angle B) = \frac{\text{opposite}}{\text{hypotenuse}} = \frac{a}{c}
\]

Thus,
\[
\sin(78°) = \frac{a}{15}
\]

We can solve for 'a':
\[
a = 15 \times \sin(78°)
\]

Using a calculator to find \( \sin(78°) \):
\[
\sin(78°) \approx 0.9781
\]

Therefore:
\[
a \approx 15 \times 0.9781 \approx 14.67
\]

So, the length of side 'a' is approximately 14.67 units.
Transcribed Image Text:### Problem Statement: In the given right-angled triangle ΔABC, angle ∠C is 90°. The vertices are labeled as follows: - A at the left-most point, - B at the top-right point, and - C at the bottom-right point where the right angle is formed. The sides of the triangle are designated as: - Side opposite to angle A (between B and C) is 'a', - Side adjacent to angle A (between A and C) is 'b', - Hypotenuse (between A and B) is 'c'. Given: - Length of the hypotenuse, c = 15 units - Measure of angle ∠B = 78° Question: - Find the length of side 'a'. ### Diagram: Here we have a right-angled triangle with: - Right angle at C (∠C = 90°) - Hypotenuse (c) connecting points A and B - Vertical side (a) connecting points B and C - Horizontal side (b) connecting points A and C. ### Solution: To find the length of side 'a', we utilize trigonometric relationships in the right-angled triangle. Given that: - \( c = 15 \) - \( \angle B = 78° \) To find side 'a', observe that in triangle ΔABC: \[ \sin(\angle B) = \frac{\text{opposite}}{\text{hypotenuse}} = \frac{a}{c} \] Thus, \[ \sin(78°) = \frac{a}{15} \] We can solve for 'a': \[ a = 15 \times \sin(78°) \] Using a calculator to find \( \sin(78°) \): \[ \sin(78°) \approx 0.9781 \] Therefore: \[ a \approx 15 \times 0.9781 \approx 14.67 \] So, the length of side 'a' is approximately 14.67 units.
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