1. Chapter 10
Section 10.1

2. Circle Definitions
A CIRCLE is a set of all points in a plane that are equidistant from a given point called the center of the circle.
A circle with center P is called “circle P” or

3. Circles
The distance from the center to a point on the circle is the RADIUS of the circle. (Segment DP is a radius)
The distance across the circle, through its center is the DIAMETER of the circle (Segment GH is a diameter)
Two circles are CONGRUENT if they have the same radius

4. Circles A CHORD is a segment whose endpoints are on the circle
A DIAMETER is a chord that passes through the center of the circle

5. Circles
A SECANT is a line that intersects a circle in two points. Line j is a secant
A TANGENT is a line in the plane of a circle that intersects the circle in exactly one point

6. Tell whether the line or segment is best described as a chord, a secant, a tangent, a diameter, or a radius of circle C.
Segment AB
Segment CD
Line EG
Segment HB

7. Interior and Exterior
In a plane, the INTERIOR of a circle contains the points that are inside the circle
In a plane, the EXTERIOR of a circle consists of points that are outside the circle

8. Tangent Circles
Coplanar circles that intersect in one point are called TANGENT CIRCLES
Coplanar circles that have a common center are called CONCENTRIC
A line or segment that is tangent to two coplanar circles is called a COMMON TANGENT

9. Tangent Circles
INTERNALLY TANGENT
EXTERNALLY TANGENT

10. Common Tangents (LINES)
A COMMON INERNAL TANGENT intersects the segment that joins the centers of the two circles
A COMMON EXTERNAL TANGENT does not intersect the segment that joins the centers of the two circles

11. Tell whether the common tangents are internal or external
Lines m and n do not intersect segment AB, so they are common external tangents
Lines j and k intersect segment CD, so they are common internal tangents