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(a) Graph \(f\) using a graphing utility. (b) Sketch the graph of \(g\) by taking the reciprocals of \(y\) -coordinates in (a), without using a graphing utility. $$f(x)=\frac{e^{x}-e^{-x}}{e^{x}+e^{-x}} ; \quad g(x)=\frac{e^{x}+e^{-x}}{e^{x}-e^{-x}}$$

Short Answer

Expert verified
Graph \( g(x) \) by reciprocating \( f(x) \); avoid \( x = 0 \) as it's undefined due to vertical asymptotes.

Step by step solution

01

Understanding the Function f(x)

The function \( f(x) = \frac{e^x - e^{-x}}{e^x + e^{-x}} \) is a hyperbolic tangent function. It can be simplified to \( \tanh(x) = \frac{\sinh(x)}{\cosh(x)} \). This function is typically used in calculus and has a range of \((-1, 1)\).
02

Graph f(x) Using a Graphing Utility

Input the function \( f(x) = \frac{e^x - e^{-x}}{e^x + e^{-x}} \) into a graphing calculator or software. You will observe that the graph approaches 1 as \( x \to \infty \) and -1 as \( x \to -\infty \). The graph is symmetric around the origin and passes through the point (0, 0).
03

Understanding the Function g(x)

The function \( g(x) = \frac{e^x + e^{-x}}{e^x - e^{-x}} \) is the reciprocal of \( f(x) \). This is equivalent to \( \coth(x) \), the hyperbolic cotangent. It's crucial to note that \( \tanh(x) \) and \( \coth(x) \) are related but have different behaviors, especially around zero.
04

Sketching the Graph of g(x) Without a Graphing Utility

To sketch \( g(x) = \coth(x) \), take the reciprocals of the \( y \)-coordinates of the function \( f(x) \). Where \( f(x) \to 1 \), \( g(x) \to 1 \) as \( x \to \infty \). Similarly, \( g(x) \to -1 \) where \( f(x) \to -1 \). However, for \( x \to 0 \), \( g(x) \) becomes undefined because the denominator of \( g(x) \) becomes zero. The graph has vertical asymptotes at \( x = 0 \).
05

Validate the Graphical Relationship

Double-check your graph of \( g(x) \). It should behave as \( \coth(x) \): it will start tall on the left, drop to cross the \( y \)-axis at a lower point, and then rise steadily on the right. Cross-check with basic known properties, ensuring \( g(x) \to 1 \) and \( -1 \) as \( x \to \pm \infty \).

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Key Concepts

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

Graphing
Graphing hyperbolic functions can be quite rewarding as it gives a visual understanding of their behavior and properties. For the function \( f(x) = \frac{e^x - e^{-x}}{e^x + e^{-x}} \), which can be rewritten as \( \tanh(x) \), the graphing process involves laying out critical points and asymptotic behavior. A graphing utility is a handy tool for quickly obtaining a precise plot. You input the function, and the output reveals that the graph approaches the lines \( y = 1 \) and \( y = -1 \) as \( x \to \pm \infty \), respectively. This graph is symmetric around the origin, indicating it has an odd function property. Observing such graphs helps solidify the understanding that \( \tanh(x) \) has a range of \((-1, 1)\) and passes through the origin. This careful observation can provide insights into how these values change as \( x \) adjusts. The graph of \( \tanh(x) \) is also smooth and continuous, reinforcing its characteristics as a core hyperbolic function.
Reciprocal Functions
A reciprocal function takes the form \( g(x) = \frac{1}{f(x)} \), representing the inverse behavior in terms of output. When dealing with hyperbolic functions, the reciprocal function can give fascinating insights. In this case, \( g(x) = \frac{e^x + e^{-x}}{e^x - e^{-x}} \), which simplifies to \( \coth(x) \). Understanding reciprocal behavior is crucial because it aids in comprehending how one function can transform into another by merely inverting its outputs. When \( f(x) \) tends toward infinity or a finite value, \( g(x) \) exhibits different limits or asymptotes. For \( \coth(x) \), note that its behavior involves infinity as \( x \to 0 \) and it approaches \( 1 \) as \( x \to \infty \). Graphically identifying the reciprocal requires observing the coordinate inversions. Where \( f(x) \approx 1 \), \( g(x) \approx 1 \), reinforcing the reciprocal nature visually.
Vertical Asymptotes
Vertical asymptotes occur in functions like \( g(x) = \coth(x) \) where the graph shoots up to infinity. These lines represent values of \( x \) where the function becomes undefined. For \( g(x) \), a vertical asymptote arises at \( x = 0 \). This point becomes undefined since the denominator \( (e^x - e^{-x}) \) equals zero at \( x = 0 \).Recognizing these asymptotes is critical as they indicate where the function's output explodes dramatically to either positive or negative infinity. Plotting these imaginary lines on a graph helps visualize where the function cannot exist and can guide students in sketching accurate graphs.Understanding vertical asymptotes will improve your skill in sketching other functions that involve division or hyperbolic concepts, as they often include such asymptotic behavior.
Symmetric Graphs
Symmetry in graphs is a strong indicator of function properties and can significantly simplify graph analysis. The graph of \( f(x) = \tanh(x) \) is symmetric about the origin, showcasing what's known as odd function symmetry.For hyperbolic functions, this symmetry means that \( f(-x) = -f(x) \). This property ensures that any point on the graph has a mirrored point on the opposite quadrant. Symmetry can be particularly useful as it allows predictions on one side of the graph to inform the other side without additional calculations. Recognizing and utilizing this symmetry can simplify understanding and working with hyperbolic functions, making them more intuitive and manageable.

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