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10.7 Assess Your Understanding

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Concepts and Vocabulary

  1. Multiple Choice The trace in the xy-plane of the graph of the equation x22y23+z24=1 is [(a) x22+z24=1, (b) x22y23=0, (c) x22y23=1].

(c)

  1. The intercept(s) of the graph of x24y29z=4 is(are) ________.

(1,0,0),(1,0,0),(0,0,4)

  1. True or False A cylinder is formed when a line moves along a plane curve while remaining perpendicular to the plane containing the curve.

True

  1. Multiple Choice The quadric surface z2=x2+y24 is called a(n) [(a) elliptic cylinder, (b) elliptic cone, (c) elliptic paraboloid, (d) hyperboloid].

(b)

  1. The quadric surface y2x2=4 is called a(n) ________.

Hyperbolic cylinder

  1. The point (0,0,0) on the hyperbolic paraboloid z=y222x252 is called a(n) ________ ________.

Saddle point

Skill Building

In Problems 7–18:

  1. (a) Identify the equation of each quadric surface.
  2. (b) List the intercepts and traces.
  3. (c) Graph each quadric surface.

  1. z=x2+y2

  1. (a) Elliptic paraboloid
  2. (b) Intercept: (0,0,0); traces: (0,0,0) in the xy-plane, z=x2 in the xz-plane, z=y2 in the yz-plane
  3. (c)
  1. z=x2y2

  1. 4x2+y2+4z2=4

  1. (a) Ellipsoid
  2. (b) Intercepts: (1,0,0),(1,0,0),(0,2,0),(0,2,0),(0,0,1) and (0,0,1); traces 4x2+y2+4 in the xy-plane, x2+z2=1 in the xz-plane, y2+4z2=4 in the yz-plane
  3. (c)
  1. 2x2+y2+z2=1

  1. z2=x2+2y2

  1. (a) Elliptic cone
  2. (b) Intercept: (0,0,0); traces (0,0,0) in the xy-plane, z=±x in the xz-plane, z=±2y in the yz-plane.
  3. (c)
  1. x2+2y2z2=1

  1. x=4z2

  1. (a) Parabolic cylinder
  2. (b) Traces x=4z2 in the xz-plane, x=0 in the xy-plane, z=0 in the yz-plane
  3. (c)
  1. x2+y2=1

  1. x2+2y2z2=4

  1. (a) Hyperboloid of two sheets
  2. (b) Intercepts: (0,0,2) and (0,0,2); traces: ellipses defined for |z|>2 parallel to the xy-plane, z24y22=1 in the yz-plane, z24x24=1 in the xz-plane
  3. (c)
  1. y2x2=4

  1. 2x=y2

  1. (a) Parabolic cylinder
  2. (b) Intercepts: z=0; trace 2x=y2 in the xy-plane
  3. (c)
  1. 4y2x2=1

In Problems 19–24, use the Figures A-F to match each graph to an equation.

  1. z=4y2x2

C

  1. 2z=x2+4y2

  1. 2x2+y2z2=1

B

  1. 2x2+y2+3z2=1

  1. y2=4x

E

  1. x2z2=y

752

Figures G–L are graphs of quadric surfaces. In Problems 25–30, match each equation with its graph.

  1. 3x2+4y2+z=0

L

  1. 3x2+4y2+4y=0

  1. 3x2+2y2(z2)2+1=0

K

  1. z24x2=3y

  1. x2+2y2z2+4z=4

J

  1. 3x2+3y2+z2=1

Applications and Extensions

  1. Explain why the graph of xy=1 in space is a cylinder.

Answers will vary.

  1. Explain why the graph of z=siny in space is a cylinder.

  1. Graph:

    1. (a) xy=1
    2. (b) z=siny
    3. (c) z=xy. (This surface is a hyperbolic paraboloid rotated 45 about the z-axis.)

  1. (a)
  2. (b)
  3. (c)

Challenge Problem

  1. Show that through each point on the hyperboloid of one sheet x2a2+y2b2z2c2=1

    there are two lines lying entirely on the surface. (Hint: Write the equation as x2a2z2c2=1y2b2 and factor.)