Chapter 14: Problem 4
Sketch the graph of the cylinder in an \(x y z-\) coordinate system. $$x^{2}+5 z^{2}=25$$
Short Answer
Expert verified
It's an infinite cylinder along the y-axis with elliptical cross-sections in the xz-plane.
Step by step solution
01
Identify the Shape
The equation given is \[x^2 + 5z^2 = 25.\]Recognize this as a standard form of an equation of a cylinder involving two variables, in this case, \(x\) and \(z\). Since \(y\) is not present, this implies that the cylinder extends infinitely in the \(y\)-direction.
02
Rewrite in Standard Form
We want to express the equation in a form where it's easier to identify the type of conic section. The equation in standard form is \[\frac{x^2}{25} + \frac{z^2}{5} = 1.\] This is similar to an ellipse equation in the \(xz\)-plane.
03
Interpret the Cross Section
Consider the cross-section of the cylinder. By setting \(y = 0\), we analyze the \(xz\)-plane: \[x^2 + 5z^2 = 25.\] This is an ellipse with the semi-major axis along the \(x\)-axis (radius 5) and semi-minor axis along the \(z\)-axis (radius \(\sqrt{5}\)).
04
Sketch the Ellipse
Draw the ellipse in the \(xz\)-plane based on the axes sizes identified: horizontal radius \(5\) along the \(x\)-axis, and a vertical radius of \(\sqrt{5}\) along the \(z\)-axis.
05
Extend along the Y-axis
Because \(y\) is not present in the equation, the complete graph of this equation in 3D is obtained by extending the ellipse in the \(xz\)-plane infinitely along the \(y\)-axis, resulting in an infinite cylinder.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
3D graphing
Three-dimensional graphing allows us to visually represent mathematical equations or objects in a coordinate system that includes three axes: the x-axis, y-axis, and z-axis. In the given problem, we're dealing with a three-dimensional object, specifically a cylinder. The equation \( x^2 + 5z^2 = 25 \) represents a standard quadratic form. However, understanding it in a 3D space requires identifying how it behaves relative to all three axes.
- The equation uses two variables, \(x\) and \(z\), without \(y\), meaning the object repeats or extends along the \(y\)-axis.
- This repetition characterizes a cylinder, which extends infinitely in one of the 3D dimensions.
ellipse cross-section
A cross-section refers to the intersection of a three-dimensional figure with a plane. For this cylinder, the cross-section can be analyzed by fixing one dimension, such as \(y = 0\). This allows us to examine the shape in the \(xz\)-plane, which resembles an ellipse.
- In the equation \( x^2 + 5z^2 = 25 \), setting \( y = 0 \) highlights the elliptical nature along \(x\) and \(z\).
- It results in an ellipse with semi-major axis (5 units) along the \(x\)-axis and semi-minor axis (\(\sqrt{5}\) units) along the \(z\)-axis.
infinite cylinder
An infinite cylinder in 3D refers to a surface extending endlessly in one direction. In this case, since \(y\) is absent from \( x^2 + 5z^2 = 25 \), the cylinder is longitudinally infinite in the \(y\)-axis direction.
- Without a boundary in the y-direction, the cylinder does not have a finite length but stretches infinitely.
- The structure is based on the repeating elliptical cross-sections perpendicular to the \(y\)-axis.
conic sections
Conic sections are curves obtained by slicing a double cone with a plane. Common examples include ellipses, parabolas, and hyperbolas. The equation \(x^2 + 5z^2 = 25\) depicts an elliptical section.
- Here, slices parallel to the base (in the \(xz\)-plane) are elliptical, as evidenced by the transformation into the form \(\frac{x^2}{25} + \frac{z^2}{5} = 1\).
- These elliptical sections are characteristic of the cylinder's mathematical structure.