Warm-Up

• Find the area and circumference of a circle with radius r = 4.

Geometry 11-1

Lines of Circles

Definitions

Example

Identify each line or segment that intersects P.

chords:

secant:

tangent:

diameter:

radii:

QR and ST

ST

PQ, PT, and PS

UV

ST

Definition

DefinitionA common tangent is a line that is tangent to two circles.

Theorem 1

• If a line is tangent to a circle, then it is perpendicular to the radius.

A

m

m is perpendicular to AB

B

Theorem 2

• If two segments are tangent to a circle from the same external point, then the segments are congruent.

ExampleRS and RT are tangent to Q. Find RS.