OBJECTIVES:

Students will be able to :

1) define various terms associated with circles

2) determine the area of a given circle

LESSON : (This could be a 1 day lesson)

A circle is the locus of points in a plane equidistant from a given point.

That point is the center of the circle. A circle is named by its center.

A radius of the circle is a segment from the center to any given point on the circle.

A diameter is a segment that contains the center of the circle and has endpoints on the circle.

In lesson # 1, the distance around a polygon is its perimeter. The distance around a circle is its circumference.

Click here for a GSP sketch to discover the relationship between the circumference and diameter

The number pi is the ratio of the circumference of any circle to its diameter.

Pi = c/d which is approximately the value 3.1415926..... or 3.14

The circumference of a circle is the product of pi and its diameter d, or C = 3.14*d.

Circumference Practice:

Find the circumference of the following circles:

Click here to check circumferences.

The area of a circle is the product of pi and the square of its radius, r, or

A = 3.14(r^2).

Area Practice:

Find the area of the following circles:

Click here to check your answers.

For more practice on circles refer to Secondary Math: Focus on Geometry, Addison-Wesley, 1996.