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Ch. 4 - Graphs of the Circular Functions
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161, 9780135440780, 9780136881117, 9780135440827, 9780135924891Non è quello che usi tu?Cambia libro di testo
Capitolo 5, Problema 40

Graph each function over a one-period interval.
y = -½ cos (πx - π)

Guida verificata passo dopo passo
1
Identify the given function: \(y = -\frac{1}{2} \cos(\pi x - \pi)\).
Recall that the general form of a cosine function is \(y = A \cos(Bx - C)\), where the period is given by \(\frac{2\pi}{|B|}\).
Calculate the period of the function: since \(B = \pi\), the period is \(\frac{2\pi}{\pi} = 2\).
Determine the one-period interval for \(x\). Since the period is 2, a natural choice is any interval of length 2, for example, \([0, 2]\) or \([-1, 1]\).
Analyze the transformations: the amplitude is \(\frac{1}{2}\) (due to the coefficient \(-\frac{1}{2}\)), the negative sign reflects the graph about the x-axis, and the phase shift is found by solving \(\pi x - \pi = 0\) which gives \(x = 1\). This means the graph is shifted right by 1 unit.

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Period of a Trigonometric Function

The period is the length of one complete cycle of a trigonometric function. For cosine functions of the form y = cos(bx), the period is calculated as 2π divided by the absolute value of b. Understanding the period helps determine the interval over which to graph the function.
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Period of Sine and Cosine Functions

Phase Shift in Trigonometric Functions

Phase shift refers to the horizontal translation of the graph caused by adding or subtracting a constant inside the function's argument. For y = cos(bx - c), the phase shift is c/b. It affects where the graph starts within the period and is essential for accurate plotting.
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Amplitude and Reflection

Amplitude is the absolute value of the coefficient multiplying the cosine function, indicating the maximum displacement from the midline. A negative coefficient reflects the graph across the x-axis. In y = -½ cos(πx - π), the amplitude is ½, and the negative sign flips the graph vertically.
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Amplitude and Reflection of Sine and Cosine