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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 53

Graph each function over a two-period interval. See Example 4.
y = -1 - 2 cos 5x

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Identify the given function: \(y = -1 - 2 \cos 5x\). Notice that it is a cosine function with amplitude, vertical shift, and frequency modifications.
Determine the period of the function. The general period formula for \(\cos(bx)\) is \(\frac{2\pi}{b}\). Here, \(b = 5\), so the period is \(\frac{2\pi}{5}\).
Since the problem asks to graph over a two-period interval, calculate the interval length as \(2 \times \frac{2\pi}{5} = \frac{4\pi}{5}\). So, the graph should be drawn from \(x = 0\) to \(x = \frac{4\pi}{5}\) (or any interval of length \(\frac{4\pi}{5}\)).
Identify key features of the graph: amplitude is \(2\) (from the coefficient of cosine), vertical shift is \(-1\) (the constant term), and the cosine function is reflected and shifted downward because of the negative signs.
Plot key points within one period by evaluating \(y\) at important \(x\) values such as \(0\), \(\frac{\pi}{10}\), \(\frac{\pi}{5}\), \(\frac{3\pi}{10}\), and \(\frac{2\pi}{5}\), then extend the pattern to cover two periods. Connect these points smoothly to complete the graph.

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