Chapter 14: Problem 58
In Exercises \(53-60,\) sketch a typical level surface for the function. $$f(x, y, z)=y^{2}+z^{2}$$
Short Answer
Expert verified
The typical level surface is a circular cylinder with radius \( \sqrt{c} \) aligned along the \( x \)-axis.
Step by step solution
01
Understand the Function
The given function is \( f(x, y, z) = y^2 + z^2 \). This function does not depend on \( x \), indicating that the level surfaces will be the same in every \( x \)-plane, which points to a cylindrical symmetry.
02
Consider the Level Surface Equation
To sketch a level surface, set \( f(x, y, z) = c \), where \( c \) is a constant. Thus, we have \( y^2 + z^2 = c \). This equation represents a circle in the \( yz \)-plane for a fixed \( x \).
03
Recognize the Cylindrical Shape
Since the equation \( y^2 + z^2 = c \) depicts circles in the \( yz \)-plane for any constant \( c \), when combined with the fact that \( x \) does not affect \( f \), the level surface is a cylinder along the \( x \)-axis with radius \( \sqrt{c} \).
04
Sketch the Typical Level Surface
For a typical value of \( c > 0 \), sketch a right circular cylinder aligned along the \( x \)-axis. The circles forming this cylinder have radius \( \sqrt{c} \) on planes parallel to the \( yz \)-plane.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Cylindrical Symmetry
Cylindrical symmetry occurs when a structure looks the same around a central axis. In mathematical terms, this means that the form or graph of a function does not change as you move around or along this specific axis. For the function you are given, \(f(x, y, z) = y^2 + z^2\), notice how there is no \(x\) in the equation. This means that whatever shape the function forms in one plane (for a fixed \(x\) value), remains the same for all other \(x\) values. Essentially, the level surfaces are `cylindrical` parallel to the \(x\)-axis, maintaining identical cross-sections at every point along the axis. This characteristic is the hallmark of cylindrical symmetry.
- Each cross-section parallel to the \(yz\)-plane is a circle.
- The radius is constant for any given level surface value.
- The symmetry makes it easier to sketch as the shape is repetitive across the \(x\)-axis.
Level Surface Equation
A level surface equation derives from taking a multivariable function and setting it to a constant. In this context, it simplifies a 3D scenario down to a more manageable graph or shape at certain values. For \(f(x, y, z) = y^2 + z^2\), if you set \(f\) to a constant \(c\), you get \(y^2 + z^2 = c\). This is a known equation of a circle. With the absence of \(x\) in the equation, you get a collection of these circles stacked infinitely along the \(x\)-axis. This leads to the creation of a cylinder.
- Equation: \(y^2 + z^2 = c\), where \(c > 0\).
- This shows how a 2D concept (the circle) becomes a 3D structure (the cylinder).
- Each \(c\) value represents a different cylinder radius of \(\sqrt{c}\).
Circular Cross-Sections
In mathematics, cross-sections help to visualize and understand the shape of a solid figure better by taking a 'slice' perpendicular to an axis. For the function \(f(x, y, z) = y^2 + z^2\), any plane parallel to the \(yz\)-plane will have a circular cross-section. When you imagine cutting through the cylinder perpendicular to its axis, each slice, or cross-section, is a circle.
- Each circle has a center at the origin of the \(yz\)-plane (0,0).
- The radius of these circles is \(\sqrt{c}\), derived from \(y^2 + z^2 = c\).
- These circles repeat consistently as you move along the \(x\)-axis.
Mathematical Visualization
Visualizing multivariable functions helps in understanding complicated structures and how different variables affect them. With \(f(x, y, z) = y^2 + z^2\), constructing a mental or physical model involves understanding how the components form a shape through symmetry, equations, and cross-sections. For this scenario:
- The absence of \(x\) compresses variety into two dimensions, making a cylinder in 3D.
- Visualizing cylinders revolves around repetitive circular patterns (as seen in cross-sections).
- Visual models can be helpful. Draw multiple circular cross-sections along \(x\)-axis to emphasize symmetry.