Chapter 12: Problem 29
Sketch the surfaces in Exercises \(13-44.\) HYPERBOLOIDS $$z^{2}-x^{2}-y^{2}=1$$
Short Answer
Expert verified
The surface is a hyperboloid of one sheet centered on the origin, opening along the \(z\)-axis.
Step by step solution
01
Identify the Surface Type
The given equation is \(z^2 - x^2 - y^2 = 1\). This is the standard form of a hyperboloid of one sheet. It is characterized by one variable being positive and the others being negative, with the right side equal to a positive constant.
02
Analyze the Traces in the Coordinate Planes
Examine the traces of the surface in the coordinate planes:- In the \(xy\)-plane (\(z = 0\)), the trace is given by \(-x^2 - y^2 = 1\), which has no real solution.- In the \(yz\)-plane (\(x = 0\)), the trace is \(z^2 - y^2 = 1\), a hyperbola.- In the \(xz\)-plane (\(y = 0\)), the trace is \(z^2 - x^2 = 1\), also a hyperbola.
03
Analyze the Horizontal Cross-Sections
Analyze horizontal cross-sections (parallel to the \(xy\)-plane) by setting \(z = c\):- The equation becomes \(c^2 - x^2 - y^2 = 1\), which suggests: - If \(c^2 > 1\), then \(x^2 + y^2 = c^2 - 1\), a circle. - If \(c^2 = 1\), it degenerates to a point circle \(x^2 + y^2 = 0\). - If \(c^2 < 1\), there is no real solution as you can't have negative radius squared.
04
Describe the Overall Shape
Based on the traces and cross-sections, the surface has a hyperboloid of one sheet structure. It opens along the \(z\)-axis and forms circles in horizontal cross-sections as \(z\) moves away from zero, indicating the shape narrows at the center and widens further along the \(z\)-axis.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Hyperboloids
A hyperboloid is a type of quadratic surface that can appear in two variations: one sheet or two sheets. In the equation \( z^2 - x^2 - y^2 = 1 \), we see an example of a hyperboloid of one sheet, which is known for having a saddle-like shape.
This surface is three-dimensional and exhibits symmetry, often looking like a stretched or compressed hourglass.
Characteristics of a hyperboloid include:
This surface is three-dimensional and exhibits symmetry, often looking like a stretched or compressed hourglass.
Characteristics of a hyperboloid include:
- It contains hyperbolas in vertical cross-sections.
- In horizontal cross-sections, it forms circles when the constant is positive and sufficiently large.
- This form has one continuous surface unlike the two-sheet hyperboloid, which consists of two disconnected parts.
Coordinate Planes
Coordinate planes play a crucial role in visualizing and analyzing multivariable calculus problems. They represent two-dimensional sections that can help simplify complex surfaces into more manageable shapes.
In the context of the hyperboloid \( z^2 - x^2 - y^2 = 1 \), examining the surface's traces in each coordinate plane provides essential insights:
In the context of the hyperboloid \( z^2 - x^2 - y^2 = 1 \), examining the surface's traces in each coordinate plane provides essential insights:
- In the xy-plane \((z = 0)\): We encounter the equation \(-x^2 - y^2 = 1\), which doesn't form a real surface, indicating the absence of a visible trace.
- In the yz-plane \((x = 0)\): The resulting equation is \(z^2 - y^2 = 1\), showing a hyperbola.
- In the xz-plane \((y = 0)\): Similarly, \(z^2 - x^2 = 1\) describes yet another hyperbola.
Hyperbola
A hyperbola is a type of conic section that is defined as the set of all points where the difference of the distances from two fixed points (foci) is constant. In a hyperboloid, the presence of hyperbolas in vertical traces reveals much about its shape.
In the case of the traces described in the equation \( z^2 - x^2 - y^2 = 1 \):
In the case of the traces described in the equation \( z^2 - x^2 - y^2 = 1 \):
- The yz-plane and xz-plane contain hyperbolas characterized by equations \(z^2 - y^2 = 1\) and \(z^2 - x^2 = 1\), respectively.
- Hyperbolas signal that the hyperboloid extends infinitely along the axes perpendicular to the axis of symmetry.
- These hyperbolas open along the z-axis since the z variable is positive in the given equation, dictating the main direction of extension.
Horizontal Cross-Sections
Horizontal cross-sections of a surface show how it behaves parallel to the xy-plane, giving insight into changes in profile as you move along the axis perpendicular to this plane.
For the hyperboloid \( z^2 - x^2 - y^2 = 1 \):When you set \( z = c \) and solve for \( x \) and \( y \):
For the hyperboloid \( z^2 - x^2 - y^2 = 1 \):When you set \( z = c \) and solve for \( x \) and \( y \):
- If \(c^2 > 1\): The equation \(c^2 - x^2 - y^2 = 1\) results in a circle, suggesting the surface broadens out.
- If \(c^2 = 1\): The equation simplifies to \(x^2 + y^2 = 0\), a degenerate circle, or essentially a single point.
- If \(c^2 < 1\): There aren't real solutions, showing that the surface thins out, disappearing.