Chapter 10: Problem 49
Graph the function with the help of your calculator and discuss the given questions with your classmates. \(f(x)=e^{-0.1 x}(\cos (2 x)+\sin (2 x))\). Graph \(y=\pm e^{-0.1 x}\) on the same set of axes and describe the behavior of \(f\).
Short Answer
Expert verified
The function oscillates between the envelope functions, with amplitude diminishing as x increases due to exponential decay.
Step by step solution
01
Understand the Function
The given function is \( f(x) = e^{-0.1x} (\cos (2x) + \sin (2x)) \). This is the product of an exponential decay function and a trigonometric function. The exponential term \( e^{-0.1x} \) governs the amplitude of the oscillation, which decays as \( x \) increases.
02
Setup the Graphing Calculator
To graph the function using a calculator, input \( f(x) = e^{-0.1x} (\cos (2x) + \sin (2x)) \). Make sure to choose an appropriate window setting that captures the oscillations and decay. A typical setting might be \( x: [0, 20] \) and \( y: [-1, 1] \) in order to clearly observe the behavior.
03
Graph the Envelope Functions
Additionally, graph the envelope functions \( y = e^{-0.1x} \) and \( y = -e^{-0.1x} \). These functions represent the maximum and minimum bounds of \( f(x) \) over time as they decay towards zero along the y-axis.
04
Observe and Analyze the Behavior
Upon graphing, observe how \( f(x) \) oscillates between the envelope functions. The function starts with a larger amplitude at \( x = 0 \) and gradually diminishes due to the exponential term. As \( x \) increases, the amplitude gets smaller and eventually approaches zero. This behavior indicates that the function is oscillating with diminishing amplitude, eventually approaching a steady state at \( y = 0 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Exponential Decay
Exponential decay is a mathematical concept where a quantity diminishes over time at a rate proportional to its current value. In the function \( f(x) = e^{-0.1x} (\cos (2x) + \sin (2x)) \), the exponential term \( e^{-0.1x} \) is responsible for the decay behavior. As \( x \) increases, \( e^{-0.1x} \) decreases, causing the overall function to shrink in amplitude. This means the peaks and valleys of the oscillating function will lessen over time.
- The base of the exponential function is the natural number \( e \), approximately equal to 2.718.
- The coefficient \(-0.1\) represents the rate of decay, indicating how fast the function decreases.
Envelope Curve
The envelope curve refers to a pair of bounding lines that frame an oscillating function. In our function \( f(x) = e^{-0.1x} (\cos (2x) + \sin (2x)) \), the envelope curves are represented by \( y = e^{-0.1x} \) and \( y = -e^{-0.1x} \). These curves define the maximum and minimum extents of the oscillations in the graph.
- The upper envelope, \( y = e^{-0.1x} \), outlines the highest points the function can reach.
- The lower envelope, \( y = -e^{-0.1x} \), defines the lowest points.
Trigonometric Oscillation
Trigonometric oscillation describes the periodic behavior of functions involving sine and cosine. In the function \( f(x) = e^{-0.1x} (\cos (2x) + \sin (2x)) \), \( \cos(2x) + \sin(2x) \) creates the oscillating pattern.
- The term \( \cos(2x) \) has a regular wave-like pattern with a period of \( \pi \), meaning it completes a cycle every \( \pi \) units.
- Similarly, \( \sin(2x) \) also contributes to the oscillatory behavior with the same periodicity and phase shift.
Graphing Calculator Techniques
Using a graphing calculator is a powerful way to visualize mathematical functions. Here are some steps to effectively graph a complex function like \( f(x) = e^{-0.1x} (\cos (2x) + \sin (2x)) \):
- Set up your calculator by correctly entering the function. This includes using the exponential and trigonometric function buttons properly.
- Choose an appropriate window setting. For this function, try \( x: [0, 20] \) and \( y: [-1, 1] \) to capture the primary behaviors within a focused range.