Chapter 10: Problem 15
Sketch the appropriate traces, and then sketch and identify the surface. $$z=\cos x$$
Short Answer
Expert verified
The surface is a cosine wave, extending indefinitely along the y-axis. The wave oscillates between -1 and 1, peaking at points where \(x = 2\pi n\) and reaching its valleys at points where \(x = \pi + 2\pi n\), with n is any integer.
Step by step solution
01
Graphing the function in 2D
The first step involves making a 2D graph of the function \(z = \cos x\). In a 2D setting, this function is a periodic function that oscillates between -1 and 1, with a period of \(2\pi\). Draw the x-axis and plot the values of \(\cos x\), marking the points where x is a multiple of \(\pi/2\) as these are key points where the function reaches its maximum, minimum, and zero-crossing points.
02
Extending to 3D
To extend the function into three dimensions, imagine the 2D graph of \(\cos x\) drawn in the x-z plane. Now, this graph will be duplicated along the y-axis. Given \(z = \cos x\) is not dependent on y, the graph will be the same for all values of y. When you sketch this, you will see a series of wave-like surfaces extending in the positive and negative y direction.
03
Identify the surface
The 3D surface for the function \(z = \cos x\) represents a wave-like form called a cosine wave, extending indefinitely along the y-axis. The peaks of this wave are located at points where \(x = 2\pi n\), with n is any integer, and the valleys occur at points where \(x = \pi + 2\pi n\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Cosine Function
The cosine function is a fundamental trigonometric function represented by the symbol \ \( \cos(\theta) \ \). It is part of the family of sine and tangent functions used commonly in mathematics, especially within geometry and calculus. \It's important to understand a few key characteristics of the cosine function: \
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- Its values range from -1 to 1. This means on a graph, the cosine function oscillates between these two points creating a wave-like shape. \
- Cosine belongs to a group of functions known as even functions. This simply implies that \(\cos(-x) = \cos(x)\), denoting symmetry about the y-axis. \
- Key points on the graph occur at multiples of \(\pi/2\), where the function reaches its peaks and troughs. \(\cos(0) = 1\ ext{ and } \cos(\pi) = -1\). Between these points, it crosses the axis at \(x = \pi/2\) and \(x = 3\pi/2\). \
Periodic Function
Periodic functions are a category of functions that repeat their values over regular intervals or periods. The cosine function is an outstanding example of a periodic function, and understanding its nature helps with sketching in 3D. \Some critical features of these functions include: \
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- Periodicity: For the cosine function \(z=\cos x\), the period is \(2\pi\). This implies that every \(2\pi\) units along the x-axis, the pattern repeats, creating cyclical waves. \
- Regularity: Because the function returns to its starting value after one period, new cycles emerge seamlessly in both 2D and 3D visualizations. \
- Applications: These functions are often found in natural phenomena such as sound waves, light waves, and ocean waves, embodying repetitive cycles. \
Wave-Like Surfaces
Wave-like surfaces in mathematics are fascinating structures often described using periodic functions like cosine. When extending a 2D cosine graph into a 3D space, wave-like surfaces are beautifully manifested. \Here's how these structures take shape and behave: \
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- The Basic Sketch: In a 2D graph, \(z = \cos x\) displays a series of undulating curves. By adding a third dimension, primarily the y-axis, these curves stretch infinitely, resulting in comprehensive wave-like formations. \
- Independence from the y-axis: For functions such as \(z = \cos x\), the value of \(z\) doesn’t change with variations in \(y\). Hence, any slice parallel to the x-z plane will show identical cosine waves. \
- Visualizing the Surface: Think of an arrangement of repeated sine waves, stacked alongside each other in the y-direction, producing a rippling effect through space. \
- Peaks and Valleys: As these waves form, peaks align where \(x = 2\pi n\) and valleys appear at \(x = \pi + 2\pi n\), creating symmetrical high and low points across the structure. \