CK-12 Geometry-Concepts

http://www.ck12.org Chapter 9. Circles

Example D

Find the value ofx.

BecauseAB⊥ADandDC⊥CB,ABandCBare tangent to the circle and also congruent. SetAB=CBand solve for
x.

4 x− 9 = 15

4 x= 24

x= 6

Watch this video for help with the Examples above.

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/52419

CK-12 Foundation: Chapter9TangentLinesB

Vocabulary

Acircleis the set of all points that are the same distance away from a specific point, called thecenter. Aradius
is the distance from the center to the outer rim of a circle. Adiameteris a chord that passes through the center of
the circle. The length of a diameter is two times the length of a radius. Atangentis a line that intersects a circle in
exactly one point. Thepoint of tangencyis the point where the tangent line touches the circle.

Guided Practice

1. Determine if the triangle below is a right triangle. Explain why or why not.