Chapter 9 -- Circles

9-1 Basic Terms

Vocabulary:

Circle: the set of points in a plan at a given distance from a given point in that plane

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Center: the given point•

Radius: (plural is radii pronounced "ray-dee-eye") the given distance. Any segment that joins the center to a point on the circle is a radius of the circle. The radius is the distance.

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Chord: a segment whose endpoints line on a circle•

Secant: a line that contains a chord•

Diameter: a chord that contains the center of the circle. The diameter is the measurement; a diameter is any chord that contains the center of the circle.

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Tangent: a line in the plane of a circle that intersects the circle in exactly one point, called the point of tangency.

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Sphere: with center O and radius r, is the set of all points in space at a distance r from point O. Spheres also have diameter, chord, secant, and tangent.

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Congruent Circles (or Spheres): circles or spheres with congruent radii.•

Concentric Circles: circles that lie in the same plane and have the same center.•

• Concentric Spheres: spheres that have the same center.

• Inscribed Polygons: a polygon that is inside of a circle and whose vertices touch the circle.

• Circumscribed Circles: a circle that is on the outside of a polygon whose vertices touch the circle.

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•touch the circle.

Examples:

Draw two tangent segments to a circle from the same point outside the circle. What do you think is true about the lengths of the segments?

1.Practice:

1. Draw a circle with center O and radius . Draw Perpendicular to . What kind of segment is ?

1. Describe the ways in which a plane can intersect a sphere.

1. Draw a sphere and several parallel planes intersecting the sphere. What are the resulting figures?

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resulting figures?

1. Is it possible to inscribe a circle in a non-rectangular parallelogram? A non-isosceles trapezoid? A non-regular pentagon?

p. 330-31 #1-17 oddHomework: get vocabulary into your notes

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