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Chapter 4: Geometry

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FIGURE 4.39<br />

The ve non-degenerate real quadrics. Top left: ellipsoid. Top right: hyperboloid of two<br />

sheets (one facing up and one facing down). Bottom left: elliptic paraboloid. Bottom middle:<br />

hyperboloid of one sheet. Bottom right: hyperbolic paraboloid.<br />

Conversely, an equation of the form<br />

Ü ¾ · Ý ¾ · Þ ¾ ·¾Ü ·¾Ý ·¾Þ · ¼ (4.18.7)<br />

defines a sphere if ¾ · ¾ · ¾ ; the center is ´ µ<br />

Ô<br />

and the radius is<br />

¾ · ¾ · ¾ .<br />

1. Four points not in the same plane determine a unique sphere. If the points<br />

have coordinates ´Ü ½ Ý ½ Þ ½ µ, ´Ü ¾ Ý ¾ Þ ¾ µ, ´Ü ¿ Ý ¿ Þ ¿ µ, and ´Ü Ü Þ µ, the<br />

© 2003 by CRC Press LLC

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