Chapter 11: Problem 25
Sketch the surfaces PARABOLOIDS AND CONES $$x^{2}+y^{2}=z^{2}$$
Short Answer
Expert verified
The surface is a bi-directional circular cone centered along the z-axis, symmetric around the origin.
Step by step solution
01
Identify the Surface Type
The given equation is a 3D surface equation usually associated with a cone. It resembles the equation of a cone in the form \(x^2 + y^2 = z^2\). This type indicates a circular cone centered along the z-axis in a 3-dimensional space.
02
Understand the Symmetry
Recognize that the equation \(x^2 + y^2 = z^2\) implies rotational symmetry around the z-axis. This means the shape will be consistent around this axis, forming a circular shape at each level of z.
03
Consider the Cross Sections
For each constant value of \(z\), the cross-section of the surface is a circle centered at the origin in the xy-plane, with radius \(z\). This is derived by rewriting the equation as \(x^2 + y^2 = z^2\), indicating for every \(z\), \(x^2 + y^2 = r^2\).
04
Sketch the Surface
Start by drawing the z-axis as the vertical axis and plot the circles corresponding to different levels of \(z\). At \(z=0\), the circle reduces to just a point at the origin. As \(z\) increases, larger circles are formed, creating the sides of the cone. This pattern extends infinitely both upward and downward, making the cone bi-directional.
05
Highlight Cone Features
Emphasize that the vertex of the cone is at the origin \((0, 0, 0)\) and the cone opens symmetrically upwards and downwards along the z-axis. This completeness around the z-axis and symmetry around the origin defines the double cone.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Conic Sections
Conic sections are shapes we get when we intersect a plane with a cone. These include circles, ellipses, parabolas, and hyperbolas. Each type is determined by the angle at which the plane cuts through the cone.
- If the plane cuts parallel to the base of the cone, it forms a circle.
- An angle more vertical than the circle but less than the angle of the side of the cone gives an ellipse.
- A plane parallel to one side of the cone produces a parabola, forming a U-shaped curve.
- When the plane cuts through both nappes (or halves) of a double cone, the shape is a hyperbola.
Rotational Symmetry
Rotational symmetry occurs when a shape looks the same after a certain amount of rotation. Imagine spinning an object around an axis, and noticing that the shape doesn't change, staying identical.
In the equation \(x^2 + y^2 = z^2\), the rotational symmetry is around the z-axis. As you rotate the cone along this axis, the shape remains consistent at every angle because each cross-section is a circle centered at the origin.
In the equation \(x^2 + y^2 = z^2\), the rotational symmetry is around the z-axis. As you rotate the cone along this axis, the shape remains consistent at every angle because each cross-section is a circle centered at the origin.
- Each circle has the same radius equal to the absolute value of \(z\).
- This symmetry gives the cone a uniform appearance no matter how it is turned around the z-axis.
Cone Geometry
Cone geometry revolves around understanding the structure and properties of cones. A cone has a circular base and a tip called a vertex. The geometry includes its volume, surface area, and other properties.
For the equation \(x^2 + y^2 = z^2\):
For the equation \(x^2 + y^2 = z^2\):
- The vertex is at the origin \((0, 0, 0)\), marking the top point of the cone.
- The cone opens along the positive and negative z-axis, making it bi-directional.
- The radius of each circular cross-section is \(z\), showing how the size changes with \(z\).
- The height between these sections varies as we move along the z-axis.