Chapter 1: Problem 67
For $$f(x)=A \sin \left(\frac{2 \pi}{B}(x-C)\right)+D$$, identify \(A, B, C,\) and \(D\) for the sine functions and sketch their graphs. $$y=-\frac{2}{\pi} \sin \left(\frac{\pi}{2} t\right)+\frac{1}{\pi}$$
Short Answer
Expert verified
A = -\frac{2}{\pi}, B = 4, C = 0, D = \frac{1}{\pi}.
Step by step solution
01
Identify Coefficient A
In the given function, the coefficient in front of the sine function determines the amplitude. For the function \( y = -\frac{2}{\pi} \sin \left(\frac{\pi}{2} t\right) + \frac{1}{\pi} \), the amplitude \( A \) is \( -\frac{2}{\pi} \). This value is taken directly from the coefficient of the sine term.
02
Identify Coefficient B
The coefficient within the sine function determines the period of the sine wave. Here, it is represented by \( \frac{2\pi}{B} = \frac{\pi}{2} \). Solving for \( B \), we have \( B = 4 \), since \( \frac{2\pi}{4} = \frac{\pi}{2} \).
03
Identify Phase Shift C
The phase shift is represented by the \( (x-C) \) term in the generic function. In the function \( y = -\frac{2}{\pi} \sin \left(\frac{\pi}{2} t\right) + \frac{1}{\pi} \), there is no \( C \) present. Therefore, the phase shift \( C \) is 0.
04
Identify the Vertical Shift D
The vertical shift \( D \) is the constant term added or subtracted from the sine function. Here, it is represented by \( \frac{1}{\pi} \), which is the constant added to the sine function. Thus, \( D = \frac{1}{\pi} \).
05
Sketch the Graph
To sketch the graph of the function, note the following characteristics: the amplitude is \( -\frac{2}{\pi} \), indicating a vertical stretch and a reflection over the x-axis; the period is \( 4 \); there is no phase shift, and there is a vertical shift of \( \frac{1}{\pi} \). The graph will oscillate between \( \frac{1}{\pi} + \frac{2}{\pi} \) and \( \frac{1}{\pi} - \frac{2}{\pi} \) with a period of 4.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Amplitude
The amplitude of a trigonometric function, particularly sine or cosine, dictates how much the function extends above and below the central axis (or midline) of the wave.This might sound complex, but it's quite simple:
Do notice that the negative sign indicates a reflection across the x-axis, but does not affect the measure of amplitude.Understanding amplitude helps predict how far and in what direction the wave will oscillate from its midline position.
- The amplitude is the absolute value of the coefficient in front of the sine or cosine function.
- In mathematical terms, if you have a function of the form \( y = A \sin(x) \) or \( y = A \cos(x) \), the amplitude is \( |A| \).
Do notice that the negative sign indicates a reflection across the x-axis, but does not affect the measure of amplitude.Understanding amplitude helps predict how far and in what direction the wave will oscillate from its midline position.
Period
The period of a sine or cosine function tells us how long it takes for the waveform to complete one full cycle and start repeating.This is a fundamental concept because it determines the horizontal stretch of the graph.
This means that the period is 4, implying the wave pattern repeats every 4 units along the x-axis.
- The formula for finding the period of a sine or cosine function is \( \frac{2\pi}{B} \), where \( B \) is the coefficient of \( x \) (or \( t \) in this problem).
This means that the period is 4, implying the wave pattern repeats every 4 units along the x-axis.
Phase Shift
Phase shift refers to the horizontal shifting of a trigonometric function's graph left or right.This shift is determined by the \( (x-C) \) or \( (t-C) \) factor within the sine or cosine function.
This means the graph remains in its standard position without any horizontal movement.
- If we have the form \( A \sin(B(x-C)) \), the graph shifts \( C \) units.
- A positive \( C \) moves the graph to the right, and a negative \( C \) moves it to the left.
This means the graph remains in its standard position without any horizontal movement.
Vertical Shift
The vertical shift of a sine or cosine wave is determined by any constant added outside the trigonometric function.This shift moves the entire graph up or down along the y-axis.
This means the entire graph is shifted \( \frac{1}{\pi} \) units upward, so its center is no longer at the x-axis but at \( y = \frac{1}{\pi} \).
- If the equation is \( y = A \sin(Bx) + D \), then \( D \) indicates the vertical shift.
- A positive \( D \) shifts the graph upward, while a negative \( D \) shifts it downward.
This means the entire graph is shifted \( \frac{1}{\pi} \) units upward, so its center is no longer at the x-axis but at \( y = \frac{1}{\pi} \).