1.9 Circles
About Circles
Pacing:This lesson could take two to four class periods
Goal:This lesson discusses numerous characteristics of circles. Inscribed polygons, equations of a circle, diameters,
secants, tangents, and chords are all presented in this lesson.
Round Robin! Once students have read through this lesson, try this fun activity. Round robin tournaments are
scheduled so each team players another exactly once. Circles and chords are used to schedule such a tournament.
Using a compass, have the students construct a circle that takes up most of an 8. 5 [U+0080][U+009D]× 11 [U+0080][U+009D]
sheet of copy paper. Decide upon a collegiate conference, such as the Big 10 and instruct students to evenly space
these dots around the circle. To do this, divide 360 ◦by11. This will give students the number of degrees before
each new dot is placed. Choosing 11 colored pencils, begin at one dot and draw a chord to a second dot (see
diagram below). Draw parallel chords until all but one team has an opponent; the leftover team has a bye. This color
represents week 1. Using a second color, start at another dot and connect it to a different team. Continue this process
until all 11 weeks have been “scheduled.”
If there is an even number of teams to be scheduled, place one dot in the center of the circle and set each remaining
dot on the boundary. Start by drawing a radius from the center to any point, then draw chords to the remaining teams.
There will be no byes with even numbered teams.
Visualization!Fill a clear bowl or container with water. Show how concentric circles are formed by dropping a rock
into water, forming ripples. Concentric circles can also be formed when raindrops hit a body of water, such as a
lake, puddle, etc.
1.9. Circles