Section 9.1 Basic terms of Circles

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Section 9.1Basic terms of Circles
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What is a circle?

• Circle set of points equidistant from the
  center
• Radius segment from the center to a point on a
  circle

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• Chord segment with endpoints on a circle
• Secant line that contains a chord
• Diameter a chord that contains the center of the
  circle

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TANGENT

• Tangent a line that intersects the circle in
  exactly one point
• Point of tangency the point where the tangent
  line intersects the circle

Point of Tang.
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Spheres

• Sphere set of all points in space at the same
  distance from the center

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Congruent Circles

• (or spheres) are circles (or spheres) that have
  congruent radii

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Concentric

• Concentric circles are circles that lie in the
  same plane and have the same center.
• Concentric spheres are spheres that have the same
  center

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Inscribed vs. Circumscribed

• Inscribed in a circle means on the inside of the
  circle.
• Try to inscribe a triangle into a circle.
• Circumscribed about a square means a circle drawn
  around a square.
• Try to circumscribe a rectangle about a circle.

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Inscribed vs. Circumscribed

• Which shape(s) are inscribed?
• Which shape(s) are circumscribed?

The square is inscribed in the circle. The
circle is inscribed in the triangle.
The triangle is circumscribed about the circle
but NOT the square. (It must hit the endpoints on
the square and it doesnt.)
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Copy the following diagram.

1. Name three radii
2. Name a diameter
3. Why is segment TK not a chord?
4. Name a tangent to circle O.
5. What name is given to point L.
6. Consider segment RS to line RS. Which is a chord
   and which is a secant?

Both endpoints arent ON the circle
Point of Tangency
Segment RS is a chord because it has endpoints.
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Practice Problems

• Page 330 W.E. 1, 4, 5, 9 15, 18