In Exercises 43–52, determine the amplitude, period, and phase shift of each function. Then graph one period of the function. y = cos(x − π/2)
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Graphs of the Sine and Cosine Functions
Problem 51
Textbook Question
In Exercises 43–52, determine the amplitude, period, and phase shift of each function. Then graph one period of the function. y = 2 cos (2πx + 8π)
Verified step by step guidance1
Identify the general form of the cosine function: \(y = A \cos(Bx + C)\), where \(A\) is the amplitude, \(B\) affects the period, and \(C\) affects the phase shift.
Find the amplitude by taking the absolute value of \(A\). In this case, \(A = 2\), so the amplitude is \(|2| = 2\).
Calculate the period using the formula \(\text{Period} = \frac{2\pi}{|B|}\). Here, \(B = 2\pi\), so substitute to get \(\text{Period} = \frac{2\pi}{2\pi}\).
Determine the phase shift using the formula \(\text{Phase shift} = -\frac{C}{B}\). Given \(C = 8\pi\) and \(B = 2\pi\), substitute to find the phase shift.
To graph one period of the function, start at the phase shift on the x-axis, then mark points at intervals of \(\frac{\text{Period}}{4}\) to capture key points of the cosine wave (maximum, zero crossing, minimum, zero crossing, maximum). Use the amplitude to determine the y-values at these points.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Amplitude of a Trigonometric Function
Amplitude is the maximum absolute value of the function's output, representing the height from the midline to the peak of the wave. For functions like y = a cos(bx + c), the amplitude is the absolute value of 'a'. In this example, the amplitude is |2| = 2, indicating the wave oscillates 2 units above and below the midline.
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Period of a Trigonometric Function
The period is the length of one complete cycle of the wave, calculated as (2π) divided by the absolute value of the coefficient 'b' in y = a cos(bx + c). Here, with b = 2π, the period is 2π / 2π = 1. This means the function repeats every 1 unit along the x-axis.
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Phase Shift of a Trigonometric Function
Phase shift is the horizontal translation of the graph, found by solving bx + c = 0 for x, giving x = -c/b. It indicates how far the graph shifts left or right from the origin. For y = 2 cos(2πx + 8π), the phase shift is -8π / 2π = -4, meaning the graph shifts 4 units to the left.
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