Chapter 5: Problem 39
Find the amplitude, period, and phase shift of the function, and graph one complete period. $$y=\sin (\pi+3 x)$$
Short Answer
Expert verified
Amplitude = 1, Period = \(\frac{2\pi}{3}\), Phase Shift = \(-\frac{\pi}{3}\).
Step by step solution
01
Identify Amplitude
The amplitude of a sine function of the form \(y = A \sin(Bx + C)\) is given by \(|A|\). In the function \(y = \sin(\pi + 3x)\), the coefficient of \(\sin\) is 1. Thus, the amplitude is \(|1| = 1\).
02
Determine the Period
The period of a sine function is given by \(\frac{2\pi}{|B|}\). Here, \(B = 3\), so the period is \(\frac{2\pi}{3}\).
03
Calculate the Phase Shift
The phase shift of a sine function \(y = A \sin(Bx + C)\) is given by \(-\frac{C}{B}\). The function \(y = \sin(\pi + 3x)\) can be rewritten as \(y = \sin(3x + \pi)\), where \(C = \pi\). Thus, the phase shift is \(-\frac{\pi}{3}\).
04
Graph One Complete Period
To graph one complete period, we start at the phase shift, \(-\frac{\pi}{3}\), and complete one full cycle within a distance of \(\frac{2\pi}{3}\). This means the function will complete one full cycle at \(-\frac{\pi}{3} + \frac{2\pi}{3} = \frac{\pi}{3}\). Plot the points starting from \(-\frac{\pi}{3}\), peaking at \(-\frac{\pi}{6}\), crossing the x-axis at 0, hitting the minimum at \(\frac{\pi}{6}\), and returning to the x-axis at \(\frac{\pi}{3}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Amplitude in Trigonometric Functions
The amplitude of a trigonometric function, such as a sine wave, represents the height of its peaks from the center line of the wave. It's a measure of how far the wave oscillates above or below the central horizontal axis.
- In mathematical terms, for a function like \(y = A \sin(Bx + C)\), the amplitude is \(|A|\), the absolute value of the coefficient \(A\).
- In the given problem \(y = \sin(\pi + 3x)\), the coefficient \(A\) is 1.
- Therefore, the amplitude is simply \(1\).
- Higher amplitude means the wave reaches higher peaks and lower valleys.
- An amplitude of 1 means a standard sine or cosine wave height in its usual [-1, 1] interval.
Understanding the Period of Sine Waves
The period of a sine function refers to the distance along the x-axis required for the function to complete one full cycle. This is an essential characteristic for understanding how frequently the wave repeats.
- For the function \(y = A \sin(Bx + C)\), period is calculated using the formula \(\frac{2\pi}{|B|}\).
- In the exercise \(y = \sin(\pi + 3x)\), the value of \(B\) is 3.
- So, the period is \(\frac{2\pi}{3}\), indicating the wave takes this length on the x-axis to loop through its full cycle.
- A shorter period means more cycles are packed into the same space.
- A longer period means the cycles are elongated, spreading apart.
Phase Shift: Shifting Trigonometric Waves
Phase shift describes how a sine or cosine wave moves horizontally from its standard position. It's the shift along the x-axis from the pattern where the function would typically start.
- For \(y = A \sin(Bx + C)\), the phase shift is given by \(-\frac{C}{B}\).
- In our function \(y = \sin(\pi + 3x)\), note that the function can be rearranged to \(y = \sin(3x + \pi)\), where \(C = \pi\).
- This gives a phase shift of \(-\frac{\pi}{3}\).
- A negative phase shift takes the wave to the left.
- A positive phase shift moves it to the right.