Geometry, Teacher\'s Edition

a. Write a hypothesis regarding measure arcCEand^6 CDE.

b. Write a hypothesis regarding the measures of^6 CDE,^6 CF E,and^6 CBE.

b. Use a protractor to measure^6 IKJ,^6 ILJ,andIHJ.

a. Write a hypothesis about an angle whose vertex is on the boundary of a circle and whose sides intersect

the endpoints of the diameter.

Angles of Chords, Secants, and Tangents

Pacing:This lesson should take one class period

Goal: This goal of this lesson is to explain the formulas for determining angle measures formed by secants and
tangents.

Vocabulary:According to http://www.encylcopedia.com, “A secant is a line that intersects a curved surface.” A chord is a
line segment connecting two points on the boundary of a circle. Thus, a chord is a segment of the secant.

Set up a chart similar to the one below to help students organize their formulas for this lesson and the next.

TABLE1.7:

Example Angle Formula Segment Length

Tangent Chord^12 (intercepted arc)

Angles formed by two in-

tersecting chords

Sum of intercepted arcs

Chapter 1. Geometry TE - Teaching Tips