Chapter 8: Problem 84
Find the function value using coordinates of points on the unit circle. $$\sin \frac{5 \pi}{6}$$
Short Answer
Expert verified
\(\sin \frac{5 \pi}{6} = \frac{1}{2} \)
Step by step solution
01
Understand the unit circle
The unit circle is a circle with a radius of 1, centered at the origin of a coordinate plane. Important angles in the unit circle are often measured in radians.
02
Determine the reference angle
Calculate the reference angle for \(\frac{5 \pi}{6}\). The reference angle for an angle \(\theta\) is the acute angle formed by the terminal side of \(\theta\) and the x-axis. For \(\frac{5 \pi}{6}\), the reference angle is \(\frac{\pi}{6}\).
03
Determine the coordinates on the unit circle
Find the coordinates of the point where the terminal side of the reference angle \(\frac{\pi}{6}\) intersects the unit circle. The coordinates for \(\frac{\pi}{6}\) are \(\left( \frac{\sqrt{3}}{2}, \frac{1}{2} \right)\).
04
Identify the sign of the sine value
Since \(\frac{5 \pi}{6}\) is in the second quadrant, and in the second quadrant, the sine values are positive, the corresponding sine coordinate for \(\frac{5 \pi}{6}\) is also positive.
05
State the sine value
Therefore, \(\sin \frac{5 \pi}{6}\) has the same sine value as \(\sin \frac{\pi}{6}\), which is \(\frac{1}{2}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Reference Angle
A reference angle helps us determine trigonometric functions in different quadrants. The reference angle is the acute angle formed by the terminal side of the angle and the x-axis. For example, for an angle \( \theta \) like \( \frac{5 \pi}{6} \), we find the reference angle by subtracting \( \pi \) from \( \theta \). This gives us the reference angle \( \frac{\pi}{6} \). Reference angles are always between 0 and \( \frac{\pi}{2} \), making them easier to work with.
Sine Function
The sine function relates the y-coordinate of a point on the unit circle to an angle. For any angle \( \theta \) on the unit circle, \( \sin(\theta) \) equals the y-coordinate of the corresponding point. For instance, with the angle \( \frac{5 \pi}{6} \), we first find the reference angle \( \frac{\pi}{6} \). The sine of \( \frac{\pi}{6} \) is \( \frac{1}{2} \). Since \( \frac{5 \pi}{6} \) is in the second quadrant, the sine value remains positive.
Quadrants
The coordinate plane is divided into four quadrants, each with different sign rules for sine and cosine values.
- First Quadrant: All coordinates are positive.
- Second Quadrant: The x-coordinates are negative, but the y-coordinates and sine values remain positive.
- Third Quadrant: Both x and y-coordinates are negative.
- Fourth Quadrant: x-coordinates are positive, but y-coordinates and sine values are negative.
Coordinate Plane
The coordinate plane helps us visualize angles and their trigonometric values. It's defined by a horizontal x-axis and a vertical y-axis. The unit circle, centered at the origin \( (0,0) \) with a radius of 1, is essential for understanding trigonometry. Each point on the unit circle represents an angle's sine (y-coordinate) and cosine (x-coordinate). For \( \frac{5 \pi}{6} \), we find the coordinates \( \left( -\frac{\sqrt{3}}{2}, \frac{1}{2} \right) \). The sine value corresponds to the y-coordinate, \( \frac{1}{2} \).