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(a) Why does the graph of \(y=\csc (x)\) have vertical asymptotes at \(x=0\), \(x=\pi,\) and \(x=2 \pi\) ? What is the domain of the cosecant function? (b) Why is the graph of \(y=\csc (x)\) above the \(x\) -axis when \(0

Short Answer

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(a) The graph of \(y=\csc(x)\) has vertical asymptotes at \(x=0\), \(x=\pi\), and \(x=2\pi\) because these are values where the sine function equals zero, making the cosecant function undefined. The domain of the cosecant function is \(x \neq n\pi\), where \(n\) is an integer. (b) The graph is above the \(x\)-axis when \(0 < x < \pi\) because the sine function is positive in this interval, and the cosecant function is its reciprocal. (c) The graph is below the \(x\)-axis when \(\pi < x < 2\pi\) because the sine function is negative in this interval, and the cosecant function is its reciprocal. (d) The range of the cosecant function is \(-\infty < y \leq -1\) and \(1 \leq y < \infty\), as it is the reciprocal of the sine function with the range \([-1,1]\).

Step by step solution

01

Recall the definition of the cosecant function

The cosecant function, denoted as \(\csc(x)\), is the reciprocal of the sine function. That is, \(\csc(x) = \dfrac{1}{\sin(x)}\). This relationship will help us reason about the properties of the cosecant function.
02

Identify vertical asymptotes

Vertical asymptotes occur when the function is undefined, which in the case of the cosecant function, is when the sine function equals zero. Thus, we need to find the values of \(x\) in which \(\sin(x)=0\). This occurs when \(x\) is an integer multiple of \(\pi\). Therefore, we have vertical asymptotes at \(x = 0\), \(x = \pi\), and \(x = 2\pi\), and similarly at all integer multiples of \(\pi\).
03

Discuss the domain of the cosecant function

The domain of the cosecant function is the set of all values for which the function is defined. Since the \(csc(x)\) is undefined whenever the sine function equals zero (i.e. at integer multiples of \(\pi\)), we can express the domain as \(x \neq n\pi\), where \(n\) is an integer.
04

Locate the graph above and below the \(x\)-axis

To determine the position of the graph in certain intervals, we can analyze the sine function in those intervals, since the cosecant function is the reciprocal of the sine function. (a) The sine function is positive for \(0 < x < \pi\), and since the cosecant function is a reciprocal, it will also be positive in this interval. (b) The sine function is negative for \(\pi < x < 2\pi\), and so the cosecant function will also be negative in this interval.
05

Determine the range of the cosecant function

The range of the cosecant function is the set of all possible values for the output of the function, i.e. all possible values of \(\csc(x)\). From the definition of the cosecant function, we know that it is the reciprocal of the sine function, which has a range of \([-1, 1]\). Therefore, the range of the cosecant function will be \(-\infty < y \leq -1\) and \(1 \leq y < \infty\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Vertical Asymptotes
The graph of the cosecant function, represented as \(y = \csc(x)\), displays vertical asymptotes because these are the points where the function is undefined. In mathematical terms, vertical asymptotes occur when the denominator of a fraction is zero.
Since the cosecant function is the reciprocal of the sine function, specifically \( \csc(x) = \frac{1}{\sin(x)} \), vertical asymptotes will appear whenever the sine function equals zero.
The sine function equals zero at integer multiples of \(\pi\). Thus, points such as \(x = 0\), \(x = \pi\), and \(x = 2\pi\), and generally \(x = n\pi\) where \(n\) is an integer, all have vertical asymptotes.
Because \(\csc(x)\) is not defined at these points, the function graph approaches infinity or negative infinity, never quite touching these lines.
Domain of Cosecant
Understanding the domain of the cosecant function involves identifying all possible input values \(x\) for which \(\csc(x)\) is defined. As previously mentioned, the cosecant function is undefined where the sine function is zero.
This means its domain excludes values like \(x = n\pi\), where \(n\) is any integer (e.g., \(0, \pm1, \pm2, \ldots\)). Therefore, the domain can be expressed as all real numbers except these integer multiples of \(\pi\).
  • Valid intervals for \(x\): \(x eq n\pi\) for integers \(n\).
  • Essentially, avoid points where \( \sin(x) = 0 \).

Keeping this in mind helps us understand that while the sine function is periodic and smooth, its reciprocal, the cosecant function, has notable interruptions at these specific points.
Range of Cosecant
The range of the cosecant function elucidates all possible output values of \(\csc(x)\). Remember, since \(\csc(x)\) is the reciprocal of \(\sin(x)\), and the sine function's range is \([-1, 1]\), the cosecant's behavior will be quite the opposite of sine.
The sine function never reaches zero within its range, ensuring \(\csc(x)\) never hovers between -1 and 1. Thus, the range comprises values drastically different from the sine’s, with factors determined by reciprocals.
  • Cosecant outputs are \(-\infty < y \leq -1\) or \( 1 \leq y < \infty \).
  • This pattern results from flipping the sine range, signifying bounded extremes with no outputs appearing between -1 and 1.

Such a separation denotes how \(\csc(x)\) sharply rises and descends whenever \(\sin(x)\) edges towards zero. These extreme angle values emphasize the impact of reciprocals on the sine-sourced range.
Sine Function Reciprocal
The cosecant function exists as the direct reciprocal of the sine function. That means wherever the sine provides a value, the cosecant gives its reciprocal: \(\csc(x) = \frac{1}{\sin(x)}\).
This relationship significantly affects how we understand and visualize the cosecant’s behavior, mainly because reciprocals transform smooth curves into steep, escalating arcs.
  • Reciprocals involve expressions flipping over an axis, highlighting a marked transformation—especially when the sine function is close to zero.
  • As the sine approaches zero, the cosecant grows large, creating its characteristic vertical asymptotes.

The significance of reciprocals is evident when predicting and explaining the cosecant graph's behavior. Simply put, where the sine is minuscule, cosecant shoots toward infinity, defining their intertwined yet distinct roles within trigonometric functions.

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Most popular questions from this chapter

(a) Use a graphing utility to draw the graph of \(y=\cot (x)\) using \(-\pi \leq\) (b) Use a graphing utility to draw the graph of \(y=\cot (x)\) using \(-2 \pi \leq\) \(x \leq 2 \pi\) and \(-10 \leq y \leq 10\)

Determine the amplitude, period, phase shift, and vertical shift for each of the following sinusoids. Then use this information to graph one complete period of the sinusoid and state coordinates of a high point, a low point, and a point where the sinusoid crosses the center line. (a) \(y=4 \sin \left(\pi x-\frac{\pi}{8}\right)\). (c) \(y=-3.2 \cos \left(50 \pi x-\frac{\pi}{2}\right)\). (b) \(y=5 \cos \left(4 x+\frac{\pi}{2}\right)+2\). (d) \(y=4.8 \sin \left(\frac{1}{4} x+\frac{\pi}{8}\right)\).

The electricity supplied to residential houses is called alternating current (AC) because the current varies sinusoidally with time. The voltage which causes the current to flow also varies sinusoidally with time. Both current and voltage have a frequency of 60 cycles per second, but they have different phase shifts. (Note: A frequency of 60 cycles per second corresponds to a period of \(\frac{1}{60}\) of a second.) Let \(C\) be the current (in amperes), let \(V\) be the voltage (in volts), and let \(t\) be time (in seconds). The following list gives information that is known about \(C\) and \(V\). \- The current \(C\) is a sinusoidal function of time with a frequency of 60 cycles per second, and it reaches its maximum of 5 amperes when \(t=\) 0 seconds. \- The voltage \(V\) is a sinusoidal function of time with a frequency of 60 cycles per second. As shown in the graphs on the next page, \(V\) "leads" the current in the sense that it reaches its maximum before the current reaches its maximum. ("Leading" corresponds to a negative phase shift, and "lagging" corresponds to a positive phase shift.) In this case, the voltage \(V\) leads the current by 0.003 seconds, meaning that it reaches its maximum 0.003 seconds before the current reaches its maximum. -The peak voltage is 180 volts. \- There is no vertical shift on either the current or the voltage graph. (a) Determine sinusoidal functions for both \(C\) and \(V\). (b) What is the voltage when the current is a maximum? (c) What is the current when the voltage is a minimum? (d) What is the current when the voltage is equal to zero?

For each of the following equations, use a graph to approximate the solutions (to three decimal places) of the equation on the indicated interval. Then use the periodic property of the trigonometric function to write formulas that can be used to approximate any solution of the given equation. (a) \(\sin (x)=0.75\) with \(-\pi \leq x \leq \pi\) (b) \(\cos (x)=0.75\) with \(-\pi \leq x \leq \pi\) (c) \(\tan (x)=0.75\) with \(-\frac{\pi}{2}

Draw the graph of each of the following sinusoidal functions over the indicated interval. For each graph, \- State the \(t\) -intercepts on the given interval. \- State the \(y\) -intercept. \- State the maximum value of the function and the coordinates of all the points where the maximum value occurs. \- State the minimum value of the function and the coordinates of all the points where the minimum value occurs. (a) \(y=\sin (t)\) with \(-2 \pi \leq t \leq 2 \pi\). (b) \(y=3 \cos (t)\) with \(-\pi \leq t \leq 3 \pi\) (c) \(y=5 \sin (t)\) with \(0 \leq t \leq 4 \pi\). (d) \(y=\frac{3}{7} \cos (t)\) with \(-\pi \leq t \leq 3 \pi\). (e) \(y=-2.35 \sin (t)\) with \(-\pi \leq t \leq \pi\). (f) \(y=-4 \cos (t)\) with \(0 \leq t \leq 6 \pi\).

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