Chapter 10: Problem 13
Use traces to sketch and identify the surface. \(x^{2}=y^{2}+4 z^{2}\)
Short Answer
Expert verified
The surface is a cone along the x-axis.
Step by step solution
01
Understand the Equation
The given equation is \(x^{2} = y^{2} + 4z^{2}\). Recognize that this is a quadratic equation in three variables which suggests it represents a quadric surface in three-dimensional space.
02
Compare with Standard Forms
The equation resembles the standard form of a cone equation: \(Ax^2 + By^2 - Cz^2 = 0\). By rewriting the equation, it closely resembles \(x^2 = y^2 + 4z^2\), which can be thought of as \(x^2 - y^2 - 4z^2 = 0\). Thus, we identify the surface as a cone.
03
Sketch the Cross-Sections
Examine the trace of the surface in various planes. For the trace in the xy-plane (z=0), the equation becomes \(x^2 = y^2\), which represents intersecting lines \(x = y\) and \(x = -y\). In the xz-plane (y=0), the equation is \(x^2 = 4z^2\), representing the lines \(x = 2z\) and \(x = -2z\). Finally, in the yz-plane (x=0), we have \(0 = y^2 + 4z^2\), the only solution is \(y = 0\) and \(z = 0\), meaning the yz-plane trace is just the origin.
04
Visualize the Surface
Recognizing the surface as a cone from the standard form and traces, visualize it as a double cone opening along the x-axis. The cross-section traces in xz and xy planes help deduce the surface's opening directions.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Cone Equation
A cone equation is a mathematical representation for cone-like structures in geometry. Its standard form can be seen as something like \(Ax^2 + By^2 - Cz^2 = 0\) or a variation, indicating a balance among square terms. The given equation is \(x^2 = y^2 + 4z^2\), and it can be rewritten in the form \(x^2 - y^2 - 4z^2 = 0\) to fall under the standard cone equation structure. Such a representation means that the resulting figure is a cone. In this case, the cone's orientation is along the x-axis, as indicated by the format of the equation. Remember, when using cone equations:
- The squared terms indicate which axis the cone is aligned with.
- Different coefficients (like the "4" in "4z^2") affect the cone's proportions and opening angle.
- Setting each variable to "0" one at a time helps identify their impact on the shape.
Traces
Traces are cross-sections of three-dimensional surfaces obtained by setting one variable in an equation to zero, or some constant. When you analyze traces of a quadric surface, you effectively "cut" through it to understand its structure. In the given equation, different traces can help visualize the conical shape:- Set \(z = 0\):The equation simplifies to \(x^2 = y^2\). This transforms into two intersecting lines, \(x = y\) and \(x = -y\), giving insights into how the cone intersects the xy-plane.- Set \(y = 0\):The equation becomes \(x^2 = 4z^2\). Solving gives lines \(x = 2z\) and \(x = -2z\). This trace in the xz-plane presents another cross-section of the cone.- Set \(x = 0\):The equation reduces to \(0 = y^2 + 4z^2\) which has a single solution at the origin. This yz-plane trace confirms no spread across axes, focusing solely on the axis of propagation.Traces are invaluable for dissecting complex surfaces into understandable slices.
Cross-Sections
Cross-sections in geometry involve slicing a three-dimensional object to produce a two-dimensional plane. In the context of quadric surfaces like cones, cross-sections reveal important shapes that help define the object. By examining traces across different planes (as we did in the earlier section):- **xy-plane Cross-Section:** Shows lines \(x = y\) and \(x = -y\);- **xz-plane Cross-Section:** Reveals lines \(x = 2z\) and \(x = -2z\);- **yz-plane (no spread):** A point at the origin confirms limited spread.These cross-sections can be envisioned as shadows or outlines when viewed from particular angles. They help predict how a three-dimensional structure looks from various perspectives. You can imagine if you were to physically cut the cone with a plane, these cross-sections are the shapes you'd see!
Three-Dimensional Space
Three-dimensional space is where we visualize objects with width, height, and depth, like the quadric surfaces in this problem. This space is mapped on three axes — usually denoted as x, y, and z. Understanding equations in three-dimensional space involves grasping how surfaces bend, twist, or spread across each axis.In this exercise, the equation \(x^2 = y^2 + 4z^2\) describes a surface that occupies three-dimensional space by forming a cone. Let’s break it down:
- The x-axis plays a central role, serving as the main axis around which the cone is centered.
- Sliced views we took as traces or cross-sections clarify how the surface reacts to each plane.
- Visualizing in 3D calls for understanding not just shapes, but also their symmetry and orientation, like the way the cone flares out along the x-axis.