1. Section 10-1 Tangents to Circles

2. Circle The set of all points in a plane that are equidistant from a given point (center). Center Circles are named by their center! P Circle P

3. Interior of a circle Consists of the points inside the circle Exterior of a circle Consists of the points outside the circle

4. L A NG E P

5. Radius The distance from the center of a circle to a point on the circle P

6. Segment whose endpoints are the center of the circle and a point on the circle All radii of a circle are congruent!

7. Two circles are congruent if they have the same radius.

8. Chord A segment whose endpoints lie on a circle

9. Diameter The distance across the circle, through the center The diameter is twice the radius

10. A diameter is a chord of a circle.

11. Secant A line that intersects a circle in two points. –I–It goes through the circle!

12. A line in the plane of a circle that intersects the circle in exactly one point, called the point of tangency. tangent

13. Tangent Line Point of Tangency

14. Chord Diameter S e c a n t P Circle P

15. Common tangent A line or segment that is tangent to two coplanar circles

16. Common internal tangent Intersects the segment that joins the centers of two circles A B

17. Common external tangent Does NOT intersect the segment that joins the centers of two circles. A B

18. In a plane, two circles can intersect in two points, one point, or no points.

19. two points of intersection:

20. One point of intersection:

22. no points of intersection:

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