Chapter 2: Problem 13
Draw the level curves (in the \(x y\) plane) for the given finction \(f\) and specified values of \(c .\) Sketch the graph of \(z=f(x, y)\) $$f(x, y)=\left(100-x^{2}-y^{2}\right)^{1 / 2}, c=0,2,4,6,8,10$$
Short Answer
Expert verified
Level curves are concentric circles decreasing in radius; surface is a hemisphere with radius 10.
Step by step solution
01
Understanding Level Curves
To draw level curves for the function \( f(x, y) = \sqrt{100 - x^2 - y^2} \), set \( f(x, y) = c \), where \( c \) are the given values 0, 2, 4, 6, 8, 10. This gives \( \sqrt{100 - x^2 - y^2} = c \), which implies \( 100 - x^2 - y^2 = c^2 \). Thus, \( x^2 + y^2 = 100 - c^2 \).
02
Identify Possible Radius
The equation \( x^2 + y^2 = 100 - c^2 \) represents a circle centered at the origin (0, 0) with radius \( \sqrt{100 - c^2} \). Calculate this radius for each \( c \) value: \( c = 0, 2, 4, 6, 8, 10 \).
03
Calculate Radii for Level Curves
For each given \( c \) value: - When \( c = 0 \), radius is \( \sqrt{100} = 10 \).- When \( c = 2 \), radius is \( \sqrt{100 - 4} = \sqrt{96} \).- When \( c = 4 \), radius is \( \sqrt{100 - 16} = \sqrt{84} \).- When \( c = 6 \), radius is \( \sqrt{100 - 36} = 8 \).- When \( c = 8 \), radius is \( \sqrt{100 - 64} = 6 \).- When \( c = 10 \), radius is \( \sqrt{100 - 100} = 0 \).
04
Sketch the Level Curves
Using these radii, draw circles in the \( xy \)-plane for each value of \( c \): - For \( c = 0 \), a circle with radius 10.- For \( c = 2 \), a circle with radius \( \sqrt{96} \), approximately 9.8.- For \( c = 4 \), a circle with radius \( \sqrt{84} \), approximately 9.2.- For \( c = 6 \), a circle with radius 8.- For \( c = 8 \), a circle with radius 6.- For \( c = 10 \), a point at the origin.
05
Sketch the Surface
To visualize the surface \( z = f(x, y) = \sqrt{100 - x^2 - y^2} \), imagine a hemisphere with its base in the \( xy \)-plane and the origin as its center. The top of the hemisphere is at \( z = 10 \), gradually decreasing to the edge of the base where \( x^2 + y^2 = 100 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Circular Level Sets
Level curves represent the connection of points where a function takes a specific constant value. In this problem, we look at the function given by \( f(x, y) = \sqrt{100 - x^2 - y^2} \). By substituting values of \( c \) into the equation \( f(x, y) = c \), we derive level curves, forming circles in the plane.
These curves center at the origin with a radius derived from the equation \( x^2 + y^2 = 100 - c^2 \). Each circle represents a distinct level set, capturing the measure of the function’s value across the xy-plane. Here, the level set turns into a point at the origin when \( c = 10 \), signifying a collapse as the height of the function, \( z \), reaches zero.
These curves center at the origin with a radius derived from the equation \( x^2 + y^2 = 100 - c^2 \). Each circle represents a distinct level set, capturing the measure of the function’s value across the xy-plane. Here, the level set turns into a point at the origin when \( c = 10 \), signifying a collapse as the height of the function, \( z \), reaches zero.
Function Plotting
Plotting \( f(x, y) = \sqrt{100 - x^2 - y^2} \) involves a combination of visualizing its level curves and overall surface in three-dimensional space. Here's how this is broken down:
- **Level Curves** form concentric circles on the xy-plane, shrinking in radius as \( c \) increases.
- **Surface View** takes a step further by imagining these circles as horizontal slices of the surface.
This surface is like a dome (or hemisphere) sitting on the base at the xy-plane.
Radius Calculation
To identify the radius of circular level curves, solve the equation \( x^2 + y^2 = 100 - c^2 \). For each constant \( c \), you calculate \( \sqrt{100 - c^2} \):
- When \( c = 0 \), the radius calculation is straightforward: \( \sqrt{100} = 10 \).
- For \( c = 2 \), it becomes \( \sqrt{96} \), which is approximately 9.8, just slightly less than 10.
- Increasing \( c \) to 4, the radius reduces to \( \sqrt{84} \), about 9.2.
- At \( c = 6 \), the radius equals 8, reflective of more shrinkage.
- With \( c = 8 \), the curve tightens further to \( \sqrt{36} = 6 \).
- Finally, when \( c = 10 \), the radius is zero: a single point at the origin.