Chapter 3: Functions of Several Variables
Section 3.3: Quadric Surfaces
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Example 3.3.2
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Put the equation into standard form for a quadric surface, identify the surface, draw its graph, and discuss the nature of the level curves and plane sections.
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Solution
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Mathematical Solution
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Figures 3.3.2(a, b) each contains a graph of the surface defined by the given equation,
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whose standard form is
obtained by completing the square in and . The standard form is the equation of a hyperbolic paraboloid with center .
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The level curves, drawn on the surface of the quadric, are the hyperbolas
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The cross sections and are parabolas, shown in Figures 3.3.2(a, b) where the sliders control the values of . Indeed, if , then the equation
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defines parabolas in the -plane, seen in Figure 3.3.2(a). Likewise, the cross sections are the parabolas
defined in the -plane, and shown in Figure 3.3.2(b).
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Figure 3.3.2(a) Hyperbolic paraboloid with cross sections
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=
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Figure 3.3.2(b) Hyperbolic paraboloid with cross sections
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Maple Solution - Interactive
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Obtain the standard form
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Control-drag the given equation.
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Context Panel: Manipulate Equation
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Check the "Show steps stacked vertically" box.
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Click the "Complete the square" button.
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Add to both sides as per the action shown in the figure below.
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Click the "Return Steps" button.
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Obtain the equivalent of the surfaces in Figures 3.3.2(a, b)
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Control-drag the given equation.
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Context Panel: Plots≻Plot Builder≻3-D implicit plot
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Set the ranges
style → surfacecontour
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3-D Options≻grid → [25, 25, 25]
scaling → constrained
lightmodel → none
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Maple Solution - Coded
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Define so that the graph of is a quadric surface
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Complete the square and put into standard form
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Obtain the equivalent of the surfaces drawn in Figures 3.3.2(a, b)
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