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Ch. 4 - Graphs of the Circular Functions
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161Not the one you use?Change textbook
Chapter 5, Problem 27

Each function graphed is of the form y = c + cos x, y = c + sin x, y = cos(x - d), or y = sin(x - d), where d is the least possible positive value. Determine an equation of the graph.


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Identify the key features of the graph such as amplitude, vertical shift, and phase shift. Since the functions are of the form \(y = c + \cos x\), \(y = c + \sin x\), \(y = \cos(x - d)\), or \(y = \sin(x - d)\), determine the vertical shift \(c\) by finding the midline of the graph (the horizontal line halfway between the maximum and minimum values).
Determine whether the graph resembles a sine or cosine function by looking at the starting point at \(x=0\). For \(y = \cos x\), the graph starts at a maximum value when \(x=0\), while for \(y = \sin x\), the graph starts at zero and increases or decreases depending on the phase shift.
Find the phase shift \(d\) by identifying the horizontal shift of the graph from the standard sine or cosine graph. The phase shift \(d\) is the smallest positive value such that the function matches the graph's horizontal displacement.
Write the equation using the identified vertical shift \(c\) and phase shift \(d\). If the graph matches a cosine function, use \(y = c + \cos(x - d)\); if it matches a sine function, use \(y = c + \sin(x - d)\). If there is no horizontal shift, \(d\) will be zero.
Verify your equation by checking if it correctly predicts key points on the graph such as maxima, minima, and zeros, ensuring the amplitude and vertical shift match the graph's features.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Amplitude and Vertical Shift in Trigonometric Functions

The amplitude of sine and cosine functions determines the height of their peaks and troughs, while the vertical shift (c) moves the entire graph up or down. Understanding these helps identify the constant c in equations like y = c + sin x or y = c + cos x by analyzing the midline of the graph.
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Phase Shift in Sine and Cosine Functions

Phase shift refers to the horizontal translation of the graph, represented by d in y = sin(x - d) or y = cos(x - d). It indicates how much the graph is shifted left or right from the standard position, and finding the least positive d helps match the given graph's starting point or key features.
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Phase Shifts

Identifying the Function Type from Graph Characteristics

Distinguishing whether the graph represents a sine or cosine function depends on key points like where the graph starts (e.g., maximum, minimum, or zero crossing). Recognizing these features allows you to select the correct base function (sin or cos) before applying shifts and vertical translations.
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Graphs of Secant and Cosecant Functions