## Reflection: Modeling Finding the Radius From a Given Circumference or Area - Section 1: Teacher Model

A more engaging way to have students learn this objective is to remove the teacher model and let students discover it.  They will find the answer by putting mathematical practice 7 to use.

Tell students:  There is a way to determine the radius and diameter of a circle when given its circumference or area in terms of PI.

Present several circumference equations and several area equations written in terms of PI. Present the radius and diameter along with the circumference or area.

Present one problem at a time on the SmartBoard.  Give students a few seconds to examine the circumference or diameter, the radius, and the diameter.  Show several before any discussion.  This will allow more kids to see the relationships between the given measures.  Have students do a turn and talk about what they see.  Students then present their thoughts which we will test out on the problem.

Some sample problems are below.

Circumference

C = 2 * PI      r = 1 d = 2

C = 4 * PI      r = 2 d = 4

C = 6 * PI      r = 3 d = 6

C = 8 * PI      r = 4 d = 8

C = 10 * PI    r = 5 d = 10

etc...

Area

A = 1 * PI     r = 1 d =2

A = 4 * PI     r = 2 d = 4

A = 9 * PI     r = 3 d = 6

A = 16 * PI   r = 4 d = 8

A = 25 * PI   r = 5 d = 10

etc...

Changing the Teacher Model
Modeling: Changing the Teacher Model

# Finding the Radius From a Given Circumference or Area

Unit 6: Geometry
Lesson 10 of 37

## Big Idea: It’s a simple lesson that allows students to focus their attention on an important skill.

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5 teachers like this lesson
Standards:
Subject(s):
Math, volume (3-D Geom), Geometry, circumference (Determining Measurements), areas, circles, determining the radius or diameter
35 minutes

### Grant Harris

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