In Exercises 61–66, use the method of adding y-coordinates to graph each function for 0 ≤ x ≤ 2π. y = cos x + cos 2x
Ch. 2 - Graphs of the Trigonometric Functions; Inverse Trigonometric Functions

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Blitzer 3rd Edition
Ch. 2 - Graphs of the Trigonometric Functions; Inverse Trigonometric Functions
Problem 62
Blitzer 3rd Edition
Ch. 2 - Graphs of the Trigonometric Functions; Inverse Trigonometric Functions
Problem 62Chapter 2, Problem 62
In Exercises 61–66, use the method of adding y-coordinates to graph each function for 0 ≤ x ≤ 2π. y = 3 cos x + sin x
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Identify the given function: \(y = 3 \cos x + \sin x\). We want to graph this function for \(0 \leq x \leq 2\pi\) by adding the \(y\)-coordinates of the individual trigonometric functions \(3 \cos x\) and \(\sin x\).
Create a table of values for \(x\) at key points within the interval \([0, 2\pi]\), such as \(0\), \(\frac{\pi}{2}\), \(\pi\), \(\frac{3\pi}{2}\), and \(2\pi\). For each \(x\), calculate \(3 \cos x\) and \(\sin x\) separately.
For each \(x\) value, add the corresponding \(y\)-coordinates: \(y = 3 \cos x + \sin x\). This means summing the values found for \(3 \cos x\) and \(\sin x\) at each \(x\).
Plot the points \((x, y)\) on the coordinate plane using the summed \(y\)-values from the previous step. This will give you points on the graph of the function \(y = 3 \cos x + \sin x\).
Connect the plotted points smoothly, keeping in mind the periodic and wave-like nature of sine and cosine functions, to complete the graph over the interval \(0 \leq x \leq 2\pi\).

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Graphing Trigonometric Functions
Graphing trigonometric functions involves plotting points based on their values at various x-coordinates, typically within one period such as 0 to 2π. Understanding the shape and behavior of sine and cosine functions helps in visualizing their graphs and how they combine.
Recommended video:
Introduction to Trigonometric Functions
Superposition of Functions (Adding y-coordinates)
When combining functions like y = 3 cos x + sin x, the graph is formed by adding the y-values of each function at corresponding x-values. This method, called superposition, helps in constructing the resultant graph by pointwise addition of the individual function values.
Recommended video:
Determining Different Coordinates for the Same Point
Amplitude and Phase Shift in Combined Trigonometric Functions
The combination y = 3 cos x + sin x can be rewritten as a single sinusoidal function with a specific amplitude and phase shift. Understanding how to find this equivalent form helps in analyzing the maximum and minimum values and the horizontal shift of the graph.
Recommended video:
Phase Shifts
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