Geometry 11-1 Circle Basics Divide your paper into eight boxes. Draw a circle in each box, but leave some room to write a definition.

Center of a circle The point in the middle of the circle. Equidistant from every point on the circle. C Radius A line segment from the center of a circle to the edge of the circle. r

Chord A line segment that connects two points on the edge of the circle. B Diameter A chord that goes through the center of the circle. d A

Secant A line that intersects a circle at two points. B Tangent A line that intersects a circle at exactly one point. A A B

Point of Tangency The point where a tangent intersects a circle. P chords: secant: tangent: diameter: radii: QR and ST ST PQ, PT, and PS UV ST Draw this is box 8

Theorem 1 If two segments are tangent to a circle from the same external point, then the segments are congruent.

Example x x – 5 AQ and AP are tangent to circle L. Determine the length of each tangent line. P Q A L

Theorem 2 If a line is tangent to a circle, then it is perpendicular to the intersecting radius. A m m is perpendicular to AB B

Example 5 cm B C Line segment AB is tangent to circle C. Determine the length of BC if the length of AB is 12 cm. A