Chapter 6: Problem 51
Graph each function over a two-period interval. $$y=-2+\frac{1}{2} \sin 3 x$$
Short Answer
Expert verified
The interval is from \(0\) to \( \frac{4 \pi}{3} \). Key points repeat every \( \frac{2 \pi}{3} \) due to periodicity of sine function.
Step by step solution
01
Understand the function components
The given function is written as \[ y = -2 + \frac{1}{2} \sin (3x) \] Identify the components: - Amplitude: \( \frac{1}{2} \) - Angular frequency: \(3\) - Vertical shift: \(-2\) These components will help in sketching the graph.
02
Determine the period
The period of a sine function \( \sin (bx) \) is given by \[ \text{Period} = \frac{2 \pi}{b} \] Here, \(b = 3\), so the period is \[ \text{Period} = \frac{2 \pi}{3} \] One period of the function is \( \frac{2 \pi}{3} \). To graph over two periods, the interval will be from \(0\) to \(\frac{4 \pi}{3} \).
03
Define key points within one period
Identify key points within one period (from \(0\) to \( \frac{2 \pi}{3} \)): - \( x = 0 \): \( y = -2 + \frac{1}{2} \sin (0) = -2 \) - \( x = \frac{\pi}{6} \): \( y = -2 + \frac{1}{2} \sin \left( 3 \cdot \frac{\pi}{6} \right) = -2 + \frac{1}{2} \sin \left( \frac{\pi}{2} \right) = \frac{1}{2} - 2 = -1.5 \) - \( x = \frac{\pi}{3} \): \( y = -2 + \frac{1}{2} \sin (\pi) = -2 + 0 = -2 \) - \( x = \frac{\pi}{2} \): \( y = -2 + \frac{1}{2} \sin \left( \frac{3 \pi}{2} \right) = -2 - \frac{1}{2} = -2.5 \) - \( x = \frac{2 \pi}{3} \): \( y = -2 + \frac{1}{2} \sin (2 \pi) = -2 \)
04
Extend to two periods
For the second period, extend the points from \( \frac{2 \pi}{3} \) to \( \frac{4 \pi}{3} \): - Calculate points similarly as those for the first period. - These points repeat because sine function is periodic.
05
Draw the graph
Plot the points on graph paper or a graphing tool. Draw smooth sinusoidal curves that pass through these points for the interval \( 0 \) to \( \frac{4 \pi}{3} \), recognizing the pattern repeats every period.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
sine function
The sine function, denoted as \(\text{sin}(x)\), is one of the fundamental trigonometric functions. It describes a smooth, periodic oscillation. The standard sine function has some characteristic properties:
- It oscillates between -1 and 1.
- It is periodic with a period of \[2\pi\].
- It starts at 0 when \(x = 0\).
amplitude
Amplitude refers to the maximum value that a periodic function reaches from its central or equilibrium value. For the standard sine function \(\text{sin}(x)\), the amplitude is 1. However, when a function takes the form \(A \text{sin}(Bx)\), the amplitude becomes the absolute value of \(A\). In our problem:
- The function is \(\frac{1}{2} \text{sin}(3x)\).
- Therefore, the amplitude is \(\frac{1}{2}\).
periodic function
A periodic function is one that repeats its values in regular intervals or periods. The most common example is the sine function, which repeats every \[2\pi\] radians.
For a sine function of the form \( \text{sin}(Bx)\), the period is altered by the value of \(B\). It is calculated using the formula:
\[\text{Period} = \frac{2\fft \pi}{B}\]. In this problem, B is 3, making the period:
\[\text{Period} = \frac{2 \pi}{3}.\] Hence, the function \( \frac{1}{2} \text{sin}(3x)\) will repeat every \(\frac{2\pi}{3} \) units. This modified period affects how the graph stretches or compresses along the x-axis.
For a sine function of the form \( \text{sin}(Bx)\), the period is altered by the value of \(B\). It is calculated using the formula:
\[\text{Period} = \frac{2\fft \pi}{B}\]. In this problem, B is 3, making the period:
\[\text{Period} = \frac{2 \pi}{3}.\] Hence, the function \( \frac{1}{2} \text{sin}(3x)\) will repeat every \(\frac{2\pi}{3} \) units. This modified period affects how the graph stretches or compresses along the x-axis.
graphing techniques
Graphing a trigonometric function involves a few basic steps:
- Identify key components: amplitude, period, phase shift, and vertical shift.
- Determine key points: start, peak, midline, trough, and end of one period.
- Extend these points to the required number of periods.
- Identify amplitude (\(\frac{1}{2}\)), period (\(\frac{2\pi}{3}\)), vertical shift (-2).
- Calculate key points within one period.
- Repeat the process for a two-period interval (0 to \(\frac{4\pi}{3}\)).
- Plot these points and draw smooth, sinusoidal curves through them.