Section 10-1 Tangents to Circles

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

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

L A NG E P

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

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

Two circles are congruent if they have the same radius.

Chord A segment whose endpoints lie on a circle

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

A diameter is a chord of a circle.

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

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

Tangent Line Point of Tangency

Chord Diameter S e c a n t P Circle P

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

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

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

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

two points of intersection:

One point of intersection:

no points of intersection:

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