Chapter 9: Problem 19
In Exercises \(15-20,\) find an equation in rectangular coordinates for the equation given in cylindrical coordinates, and sketch its graph. $$ r^{2}+z^{2}=4 $$
Short Answer
Expert verified
The equivalent equation in rectangular coordinates is \( x^2 + y^2 + z^2 = 4 \), which represents a sphere with the centre at the origin and radius 2.
Step by step solution
01
Understanding Cylindrical and Rectangular Coordinate systems
The rectangular coordinate system is based on x, y and z coordinates while the cylindrical coordinate system uses r, θ and z where r is the radius in circular base (which is formed by x and y in rectangular), θ is the angle formed by x-axis and line from origin to the point in base and z is height or depth from this base.
02
Converting the given cylindrical coordinates to rectangular coordinates
The given equation is \( r^2 + z^2 = 4 \). In the cylindrical coordinate system, the radius r in the circular base is given by \( r = \sqrt{x^2 + y^2} \). By substituting this into the given equation, we get \( (\sqrt{x^2 + y^2})^2 + z^2 = 4 \). Simplifying this gives \( x^2 + y^2 + z^2 = 4 \).
03
Identifying the graph of the equation
This equation represents the equation of a sphere in three dimensions. The sphere has a center at the origin (0,0,0) and has a radius of 2, since 4 is the square of the radius of the sphere. Therefore, the graph would comprise of a sphere centered at origin and having radius equal to 2.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Rectangular Coordinates
Rectangular coordinates, often called Cartesian coordinates, form the basis for a three-dimensional graphing system. They use three values: \(x\), \(y\), and \(z\), which represent length along the respective axes.
These coordinates help locate points in 3D space by using a combination of these values:
These coordinates help locate points in 3D space by using a combination of these values:
- The \(x\)-coordinate determines the position along the horizontal axis.
- The \(y\)-coordinate identifies the position along the vertical axis.
- The \(z\)-coordinate indicates height or depth from the \(xy\)-plane.
Equation Conversion
Equation conversion is an essential concept when transitioning from one coordinate system to another. In this context, it often involves switching from cylindrical to rectangular coordinates.
While converting:
While converting:
- The radius \(r\) in cylindrical coordinates transforms to \(\sqrt{x^2 + y^2}\) in rectangular terms, connecting the relationship between these coordinates.
- Values such as \(\theta\) are not directly visible in basic three-variable expressions; thus, the focus usually remains on translating radial distances and altitudes into \(x, y, z\) components.
Sphere Equation
A sphere is a classic geometric shape in three-dimensional space and is easily represented in both cylindrical and rectangular coordinates. The equation of a sphere in rectangular coordinates is given by:\[x^2 + y^2 + z^2 = r^2\]where \(r\) is the radius of the sphere.
In our exercise, the equation \( x^2 + y^2 + z^2 = 4 \) describes a sphere centered at the origin with a radius of 2, because 4 is the result of squaring the radius.
In our exercise, the equation \( x^2 + y^2 + z^2 = 4 \) describes a sphere centered at the origin with a radius of 2, because 4 is the result of squaring the radius.
- The center of the sphere at the origin is noted as \((0, 0, 0)\).
- The radius is derived by recognizing that \(r^2 = 4\), leading to \(r = 2\).
3D Graphing
3D graphing is a powerful tool that allows for the visualization and analysis of equations in three-dimensional space.
When graphing three-dimensional objects like spheres:
By plotting such equations, students gain an understanding of both the mathematical and tangible nature of three-dimensional objects. Mastering 3D graphing enhances skills in spatial reasoning and further applications in engineering, architecture, and natural sciences.
When graphing three-dimensional objects like spheres:
- Tools like 3D modeling software or graphing calculators help in visualizing equations.
- Axes need to be labeled properly to distinguish \(x\), \(y\), and \(z\).
- Graphs can represent physical models or concepts that have 3D implications.
By plotting such equations, students gain an understanding of both the mathematical and tangible nature of three-dimensional objects. Mastering 3D graphing enhances skills in spatial reasoning and further applications in engineering, architecture, and natural sciences.