Chapter 14: Problem 22
Graph the curves described by the following functions, indicating the positive orientation. $$\mathbf{r}(t)=2 \cos t \mathbf{i}+2 \sin t \mathbf{j}+2 \mathbf{k}, \text { for } 0 \leq t \leq 2 \pi$$
Short Answer
Expert verified
Answer: The curve is a circle of radius 2 in the plane parallel to the x-y plane at a height of z=2. Its orientation is positive, which means it is counter-clockwise when viewed from above the plane.
Step by step solution
01
Identify parametric equations for x, y, and z
The given function is in vector form. We need to extract the parametric equations for x, y, and z as follows:
$$x(t) = 2\cos(t)$$
$$y(t) = 2\sin(t)$$
$$z(t) = 2$$
These parametric equations indicate the position of each point on the curve with respect to t.
02
Understand the pattern of the curve
The parametric equations for x and y look like the equations for a circle with radius 2 centered at the origin in the x-y plane. The z(t) part remains constant at 2.
As t varies from \(0\) to \(2\pi\), the x(t) and y(t) will trace a circle of radius 2 in the x-y plane, while the z(t) will remain constant at 2 units above the x-y plane. Thus, the curve is a circle of radius 2 in the plane parallel to the x-y plane at a height of z=2.
03
Plot the curve with positive orientation
Now, we will plot the curve with a positive orientation. Since the x(t) and y(t) follow a circular pattern, the positive orientation would be counter-clockwise.
1. Start at t=0, which gives us the point (2,0,2).
2. As t increases from 0 to \(\frac{\pi}{2}\), we move counter-clockwise along the circle in the x-y plane, while maintaining z=2.
3. The complete curve is formed when t reaches \(2\pi\), and we are back to the starting point (2,0,2).
By following these steps, we can visually plot the curve described by the function, while indicating the positive (counter-clockwise) orientation around the circle in the plane parallel to the x-y plane at z=2.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vector Functions
In mathematics, vector functions play a crucial role in describing curves in space. A vector function essentially provides a way to express a curve through a set of ordered components, typically represented as \( \mathbf{r}(t) = x(t) \mathbf{i} + y(t) \mathbf{j} + z(t) \mathbf{k} \). This notation uses the standard unit vectors \( \mathbf{i}, \mathbf{j}, \) and \( \mathbf{k} \) corresponding to the x, y, and z axes, respectively.
For our exercise, the vector function \( \mathbf{r}(t) = 2 \cos t \mathbf{i} + 2 \sin t \mathbf{j} + 2 \mathbf{k} \) provides a three-dimensional description of the curve. The components of this vector function \((x(t), y(t), z(t))\) tell us how the curve moves through space as the parameter \( t \) changes. Here, \( t \) acts like a time or progression variable, which when incremented, draws the path of the curve.
For our exercise, the vector function \( \mathbf{r}(t) = 2 \cos t \mathbf{i} + 2 \sin t \mathbf{j} + 2 \mathbf{k} \) provides a three-dimensional description of the curve. The components of this vector function \((x(t), y(t), z(t))\) tell us how the curve moves through space as the parameter \( t \) changes. Here, \( t \) acts like a time or progression variable, which when incremented, draws the path of the curve.
- Each component \( x(t), y(t), \) and \( z(t) \) tells about the path's coordinates in space.
- Understanding the vector function helps to visualize and interpret the motion along the curve in 3D.
- It aids in translating complex motions or shapes into simpler mathematical expressions.
Parametric Equations
Parametric equations facilitate the representation of curves by defining a set of functions in terms of a parameter \( t \). Unlike standard Cartesian equations which represent curves by relating x and y directly, parametric equations allow for more complex and flexible representations.
In the original exercise, we derived 3 parametric equations from the vector function \( \mathbf{r}(t) \):
- \(x(t) = 2 \cos t\) and \(y(t) = 2 \sin t\) describe a circle in the x-y plane. This holds because the expressions mimic those of a circle's parametric form: \( x = r \cos(t) \) and \( y = r \sin(t) \).- \(z(t) = 2\) shows the height remains constant, illustrating that the circle is parallel to the x-y plane but elevated at z = 2.
These parametric equations allow us to plot more complex curves and analyze them through each section of 3D space based on the parameter \( t \). Parametric equations are valuable for:
In the original exercise, we derived 3 parametric equations from the vector function \( \mathbf{r}(t) \):
- \(x(t) = 2 \cos t\)
- \(y(t) = 2 \sin t\)
- \(z(t) = 2\)
- \(x(t) = 2 \cos t\) and \(y(t) = 2 \sin t\) describe a circle in the x-y plane. This holds because the expressions mimic those of a circle's parametric form: \( x = r \cos(t) \) and \( y = r \sin(t) \).- \(z(t) = 2\) shows the height remains constant, illustrating that the circle is parallel to the x-y plane but elevated at z = 2.
These parametric equations allow us to plot more complex curves and analyze them through each section of 3D space based on the parameter \( t \). Parametric equations are valuable for:
- Describing motions in physics, where time as a parameter showcases position changes of objects.
- Engineering and computer graphics, allowing for precise control and animation of shapes and paths.
- Mathematical analysis of curves and surfaces, enhancing insight beyond what standard equations provide.
3D Plotting
Three-dimensional plotting is an exciting way to visualize mathematical concepts and their spatial relationships. By plotting in 3D, you can inspect curves, surfaces, and shapes from different angles, offering a more intuitive grasp of their form and function.
With the parametric equations derived \( x(t) = 2 \cos t \), \( y(t) = 2 \sin t \), and \( z(t) = 2 \), we plot a circle in a plane parallel to the x-y plane at \( z = 2 \). The circle is drawn using the radius of 2, starting from the point (2,0,2) when \( t = 0 \), and completing back to the same point as \( t \) reaches \( 2\pi \).
Consider these steps for effective 3D plotting:
The value of 3D plotting is particularly significant in fields such as:
With the parametric equations derived \( x(t) = 2 \cos t \), \( y(t) = 2 \sin t \), and \( z(t) = 2 \), we plot a circle in a plane parallel to the x-y plane at \( z = 2 \). The circle is drawn using the radius of 2, starting from the point (2,0,2) when \( t = 0 \), and completing back to the same point as \( t \) reaches \( 2\pi \).
Consider these steps for effective 3D plotting:
- Begin by setting up a 3D graphing environment where axes are defined as x, y, and z.
- Plot points for varying \( t \) from \( 0 \) to \( 2\pi \) to draw the circle in the 3D space.
- Ensure the plotted curve accurately captures the positive orientation, in this case, counter-clockwise.
The value of 3D plotting is particularly significant in fields such as:
- Engineering designs, allowing the modeling of complex parts and systems in three dimensions.
- Medicine, where anatomical structures are visualized accurately.
- Graphics and simulation industries, driving realistic animations and environmental renderings.