Chapter 10: Problem 6
Find the exact value or state that it is undefined. $$ \sec \left(-\frac{3 \pi}{2}\right) $$
Short Answer
Expert verified
\(\sec \left(-\frac{3 \pi}{2}\) is undefined because it involves division by zero.
Step by step solution
01
Determine the Reference Angle
The angle \(-\frac{3 \pi}{2}\) can be converted into a positive angle by adding \(2\pi\) until we fall into the range of a full rotation \([0, 2\pi)\). Since \(2\pi = \frac{4\pi}{2}\), we have \(-\frac{3\pi}{2} + 2\pi = \frac{\pi}{2}\). The reference angle is \(\frac{\pi}{2}\).
02
Understand the Position on the Unit Circle
In the unit circle, \(\frac{\pi}{2}\) corresponds to the point (0, 1) on the circle since it is at the top of the vertical axis. Here, the cosine of \(\frac{\pi}{2}\) is 0.
03
Recall the Definition of Secant
The secant function is defined as the reciprocal of the cosine function. Thus, \(\sec \theta = \frac{1}{\cos \theta}\). Here, \(\cos \frac{\pi}{2} = 0\).
04
Evaluate the Secant for the Angle
Since \(\cos \frac{\pi}{2} = 0\), the reciprocal, given by \(\sec \frac{\pi}{2} = \frac{1}{0}\), does not exist. Division by zero is undefined in mathematics.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Unit Circle
The Unit Circle is a fundamental concept in trigonometry. It helps us understand angles and their corresponding sine, cosine, and tangent values. The unit circle is a circle with a radius of 1 unit centered at the origin of a coordinate plane.
A key feature of the unit circle is that for any given angle, the x-coordinate of the point on the circle represents the cosine of that angle, while the y-coordinate represents the sine. These coordinates are crucial when working with trigonometric functions.
To find angles on the unit circle:
A key feature of the unit circle is that for any given angle, the x-coordinate of the point on the circle represents the cosine of that angle, while the y-coordinate represents the sine. These coordinates are crucial when working with trigonometric functions.
To find angles on the unit circle:
- Angles are measured in radians, though degrees can also be used.
- The full circle represents a complete rotation of either 360 degrees or \(2\pi\) radians.
- Commonly used angles include \(\frac{\pi}{2}\), \(\pi\), \(\frac{3\pi}{2}\), and \(2\pi\), situated at important points in the unit circle.
Secant Function
The Secant Function is a trigonometric function related closely to the cosine function. It is defined as the reciprocal of the cosine function. Simply put, for any angle \(\theta\), the secant is given by:
To know the secant function better:
- \( \sec \theta = \frac{1}{\cos \theta} \).
To know the secant function better:
- The secant values become larger as the cosine approaches zero from either side of the circle.
- While \( \cos \theta \) ranges from -1 to 1, \( \sec \theta \) can take values from negative or positive infinity whenever cosine is zero.
- The secant function is especially important when addressing problems involving vertical asymptotes, as it tends to infinity at those points.
Reference Angle
A Reference Angle is a crucial tool when dealing with angles in trigonometry. It is the acute version of an angle, always between 0 and \( \frac{\pi}{2} \), that shares the same terminal side in standard position.
How to calculate a reference angle:
How to calculate a reference angle:
- If an angle is in the first quadrant, the reference angle is the angle itself.
- In the second quadrant, subtract the angle from \( \pi \).
- For the third quadrant, subtract \( \pi \) from the angle.
- In the fourth quadrant, subtract the angle from \( 2\pi \).